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This is im harmony with tbe fact that the mercury appears as the free metal at the end of the reaction. This deposit is a good conductor of eteetncity but does not amatgamate with mercury. H8, , The problem is of theoretical tather than immediate practica! Cases are known ia whtch this hydration takes place under the iaNttence of dilute add atone. Such a case is that of ptpefonyt acelyteme whieh gives the eotrespondinx ketone on wanaiN: with ditute hydrochloric add. Hg OR X. Neither fonnuJa explains ail of the reactioas.

Acids and alkyl ha! Vanoas teactions give formic acid derivatives, a fact which is hard to explain by the second formula. The same teagents give another ptoduct wh! In an. He ptaces the mercury compound in an iron crucible, covers it with a mixture of barium and sodium carbonates, and heats very gentiy. Bancroft ConteatmtioB by Ptetatioa. Rickard beHeves, pp. That is the conclusion that mostseientMc men wHi reach, though it apparentiy cannot be proved iegaMy.

What ls needed is a suf5cient! It happens to be easier to secure this with substances which lower the surface tension of water; but that does not affect the general theory. Dureti says, p. A hypothesis based on nascent and ocduded gas explains aii kinds of Notation as well as notation machines. In the same article, p. DureM says "that an acid or any electrolyte creates osmotic pressure, by trying to enter the solid. If this pressure be suffident to drive most of the gas out from the gangue particles, the tnetaiHc partides can be Noated, for the reason that there is stiM ieft MuSdent gas in them to become nuclei for bubble formation by the nascent gas of the Mquid Everyone who bas experimented with ftotation bas seen how too much acid wiii 'MH' the Noat.

In maintainiag that osmotic pressure of an electrolyte is the cause of selective flotation, it is weU to look into the motive power of osmotis. However, ail theories of Notation, be they electrical or otherwise, must come to osmosis for their solution. There seems to be ao good reason to suppose that an electrolyte, as sueh. Bvea, then, it is not clear what itaportaatpartispiayedbyosmosh. It temains to be seen how Minerab Separation wH!

Rickard also states bis bdief that "the validity of the patent for a soluble frothing agent should be fought to a finish and it shouid be ascertained what is a'soluble frothing agent' and whether tt is covered by the description of the oit ia the first patent. The chapter on metallurgy takes up iron and steet. One does not see why the lead storage battery should corne in under metaNNrgy.

The reviewer doubts the statement p. F , which is found in Greentand as the minerai cryoUte, gave mdted metaUie atumiamn. Gortaer, R. Re: 13, , Fix. W: On the cOXddat sweuing of wheat gluten. Upson, P. The problem therefore is a deeper ope than merely a study of the action of salts or acids on the physical properties of a colloid. It is a theorem in colloid chemistry that a colloidal system has a "memory," that the colloidal behavior of an emulsoid sol or an emulsoid gel is dependent not alone upon its present environment but upon its past history, and it would seem that the past history of the gluten while it is beiag deposited in the endosperm of the wheat berry is the detennining factor of a strong or of a weak nour.

Such papers as bear upon the subject under consideration will be considered from time to time as latep papers are prepared for publication. OstwaM, W. Uber koMoM. KoU Ze:t. ZurVbkosimetde der Mehle. MeM, H. LOen, H. Beitrage zur KoNoidchemie des Bfotes. These workers make no mention of the work by Gortner and Doherty and they, like Upson and Calvin, reason from analogy rather than from actual experiments made upon both strong and weak t[ours. For example, Cohn and Henderson'" state, "The 'body' of the dough is supplied by the wheat gluten alone. The degree to which the dough can be distended therefore depends upon the amount and the hydration of the gluten.

It is impossible to determine from the data given in the papers of Henderson, et al. The physical chemistry of bread making. Sdence, 48, H: On the control of rope in bread. Hendersoa, L. H-, WachnMN, J. Unfortunately no nitrogen detenninations are available, nor is the source or grade of the samples noted. He finds for the flours which he investigated that "flours with high gas-retaining capacities and high bakers' marks have been shown to be those in which the 'amended gliadin' figure is high.

It would be interesting to know whether or not the proteolytic enzyme activity MfMd with the different flours which Martin used. In one of the flours which he worked with he showed that there was appreciable proteolytic activity. He a1so pointed out that the diastatic activity varied with the If Martin, P. Unfortunately none of the flours with which Gortner and Doherty worked were available for the present series of investigations.

Consequently it became necessary to repeat at least a part of their work using gluten from new samples of flours in order that the comparative data for the present set of flours would be complete. Imbibition in the presence of different strengths of the following alkalies: potassium hydroxide, sodium hydroxide, calcium hydroxide, barium hydroxide and ammonium hydroxide.

Theoptimum hydrogea ion concentration for the swelling of dises in. B is a first clear flour made in the same. B 0. It was thought advisable to repeat the bakings with flours B and B and also inasmuch as a low volume might be due to deficiency of soluble carbohydrates to investigate the effect of diastase. Jessen-Hansea'" has pointed out that the optimum hydrogen ion concentration for baking is around pH value of 5. Comptes-rendus des Travaux Lab. Itisregrettedthatthesupplyoffioursdid not permit fufther tests along this Une, but the tests tend to show the superiority of flour B H: A metttod for the determination of the strength and baking quaUtiesof wheat NoNr.

Potass1um Sulfate-Soluble Protein. Two 50 ce aliquots were taken and protein determined as above. The material was filtered and the protein content determined as above. At the end of this time the material was filtered and nitrogen determined on aliquots of the filtrate. The residue remaining was then treated with a fresh portion of potassium sulfate solution and the process repeated. This extraction was continued until six separate portions of potassium sulfate solution had been used or a total of about ce.

Protein was determined on the total alcohol extract by the Kjeldahl method as described above. These determinations were ail carried out in duplicate. The average of the different determinations is given in Table III. More dimculty was evidenced in collecting the gluten from B; it was rather intermediate between B and B and B They were whiter, it was harder. Protem obtained by N X 5. F our Ptouf. It is particularly interesting to compare the data for B and B, the "strongest" and the "weakest" samples studied.

The ash values are not widely different and are indicative of a "patent" and a "straight" flour. The crude protein values are almost identical so that, in this instance at least, the "weakness" of B does not lie in a lower gluten content. The marked contrast in the baking tests shows that in these contrasting samples we have excellent material for testing as to whether or not the differences observed in the baking tests are paralleled by differences in the physicochemical behavior of the glutens.

The Preparation of Dried G'M. Using dried material. Therefore the attempt was made to prepare considerable quantities of the dried glutens washed from the four flours. Consequently the drying must necessarily be carried out at a temperature that would not be at a11 unfavorable to bacterial and enzyme action. About 3 kilos of flour were made into a stiff dough with distilled water and allowed to stand under distilled water for an hour. The material was then placed in an electrically driven dough-mixing machine.

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Distilled water under considerable pressure was run continuously into the mixer at a rather rapid rate. At the end of about 7 minutes atl of the starch appeared to have been removed, the liquid from then on remaining only slightly turbid; the treatment was continued for 13 minutes longer, the water by this time had begun to froth slightly. Glass plates were used for shelves in the vacuum oven and these little squares were placed on the glass plates at least 1 centimeter apart. It was possible to dry the material to a crisp in less than 18 hours by this method, the drying was, however, continued for a total of 48 hours.

This material showed no evidence of decomposition that could be detected by odor. The percentages of moisture and crude pro- tein are reeorded in Table IV. Lab no Mobtwe. Crudeprotein ia. From their data it is evident that two types of results may be expected, i. We have felt that it would not be profitable to repeat. The dises of gluten were al-. KOM Yt. Imbibition Penod 50 Minutes. Average of 5 Determinations. Conceutratiou B B B B of acid.

The Imbibition curves for the various gtuteas in different concentra-. It will be observed that there is a wide difference in the imbibitional capacity of glutens B Twenty grams of the dried gluten. Imbibition Period 50 Minutes. The top curve fs B. Imbibition Pencd 25 Minutes. Average of 5 Detenninations.

Concentmttott —————————————— —————— of acid Before After Before Befofe dfyiag dtyimg drying drying. SOt 0. It is of interest to note that in the 50 minute experiments B' has decreased in its imbibing capacity in lactic acid to a very appreciable extent, that. B has decreased somewhat but the other two glutens have not changed to so marked a degree. This appears to indicate that the glutens are tending to become alike. In ail of the glutens the concentration of add necessary to produce maximum imbibition has likewise increased.

It bas been our experience that weak glutens reach their point of maximum imbibition only in a higher concentration of acids than do strong glutens, and in the present instance the drying process appears to have produced a "weak" gluten as measured by rate and extent of imbibition. A series of sodium hydroxide solutions was prepared of the same normalifies as those employed m the study of the acids. It was impossible to remove the dises at the end of the imbibitional period, ail coherence having been destroyed.

In the case of the more dilute alkaline solutions the discs were coherent enough to be removed for weighing. In order to ascertain whether or not this was a case of complete. This showed conclusively that the gluten was in reality being dispersed and by the amount of precipitate one would conctude that the process was going on rather rapidly. It woutd seem that the action of alkalies on gluten is somewhat different from the action of the acids.

In the case of acids the first step is the swelling of the gluten with no apparent dispersion. In no instance was there more than a slight turbidity produced. In the case of acid there is marked imbibition as shown by appearance and by the increase in weight. In the case of alkali however the two steps, imbibition and dispersion, follow one another almost immediately so that in some concentrations they compensate each other. In the more dilute solutions the imbibitional factor is the more prominent, in the more concentrated solutions the dispersion factor is the most apparent.

No appreciable imbibition was noted however. In an attempt to make the imbibition factor more prominent the time for the swelling determination in the presence of alkalies was shortened from 50 minutes to 25 minutes. A comparison of the results obtained in these two time intervals is shown in Table XI. It was concluded from Table XI and the swelling size as shown by appearance that 25 minutes would indicate the imbibition factor more accurate!

The imbibition of the different glutens was studied in so. Avefage of 10 Detenainations. ConceatMtioaofatkaU 60 minutes zs miaMtes. Gluten for the Vatious Glutens before dfying io Different Con-. Imbibition period 25 Minutes. In the higher concentrations the dispersion factor is more prominent as shown by the fall in the curve. B and B behaved in ail respects like gluten B with the exception that the dispersion was more marked in the case of B and B Thts and is shown very clearly in Fig.

This dough was aUowed to stand under distilled water for one hour and was then washed in a stream of distilled water. As soon as the washing was begun, however, the gluten began to disperse. This was tried repeatedly with the dried glutens from the different flours. It was found, however, that if a very small amount of sodium chloride was added to the wash water the gluten immediately came together in a coherent mass whieh showed greater elasticity than the gluten before drying. If the coherent mass obtained by washing in sodium chloride solution was washed in distilled water it began to disperse but was easily brought to a coherent mass by again washing in the salt solution.

This process was repeated several times with the same sample and probably could be repeated indefinitely. The method finally adopted was to add enough water to make a dough and let this dough stand under distilled water for one hour The material was then pressed into sheets without working. Water — 0. The method finally adopted for the study of imbibition of the dried glutens was the same as that employed in the work with dried glutens and acids, i. Although a rather extensive series of experiments was carried out it was found that no method could be devised whereby imbibitional values could be obtained with the dried glutens which were free from large errors due to dispersion.

Consequently it is not thought worth while to record the tabular data. The experiments, however, emphasize rather strongly the marked changes in colloidal condition which occur in drying the glutens and confirm the conclusions arrived at in the earlier sections where imbibition of dried and undried glutens in acid solutions is considered.

The Etfeot of Calcium and Potassium Hydroxides eontaic. It is weU known that neutral salts markedly decrease imbibition of proteins in acid or alkaline media. Gortner and Doherty I have already presented data showing that wheat gluten is no exception to this general ruie, at least in so far as acids are concemed. The imbibition cuives for the glutens B. The results are in good accord with the depressing effect of salts upon imbibition in acids and it was not thought worth while to conduct any further experiments to show the effect of salts inasmuch as their effect has been shown on so many proteins by many different workers.

The present series of experi-. Concentrations of Calcium Hydroxide. Imbibition Period 25 Minutes. By the use of this method curves are obtained of radically different shapes with the different acids used of which hydrochloric represents the one extreme and acetic acid perhaps the other, as shown in Figures 1 to 5 in the article of Gortner and Dohertyl and in Figures 1 and 2 of this paper.

Loeb, J. We have, therefore, determined by the potentiometric method the hydrogen ion concentration of the various solutions of lactic, acetic, orthophosphoric, hydrochloric and oxanc acids in the dilutions used by Gortner and Doherty. A Leeds and Northrup potentiometer was used for the measurement of the voltage. A Type R high sensitivity galvanometer was used as a current detector, and the hydrogen electrodes were of the Bailey" type. A normal KCt calomel electrode and a flowing junction of sat. KCI were used.

Univefsity of California Publications in Physiology, 5, No. Mareh 29 Retative Imbibition of Glutens "P" and "Wi! M t M t 1 Grams of water ttMMbed per gram. NonnaUtyof pHofaodsoiu- ofmoiststutea. In the case of the strong acids white giving a relatively high concentration of hydrogen ions at the point of greatest imbibition the titratable acidity is relatively low.

In order to increase the hydrogen ions in the inunediate vicinity of the dise it is necessary that diffusion should act over a relatively great distance. In the case of the weaker acids the high point of the imbibition curve oc. The weak acids by their buffer action tend to repleaish the solution with hydrogen ions as fast as depleted by the dise. For this reason the maximum point of imbibition for the weak acids seems in general to occur at a lower hydrogen ion concentration than is the case with the strong acids.

Further data on this part will be included in a later paper. In order to more directly compare the effect of acids and alkalies on the imbibitional rate, imbibitional experiments were carried out for 25 minute intervals in solutions of lactic and hydrochloric acids. These results indicate that under the same conditions the effect of the acids is somewhat greater than is the effect of alkalies.

This was also shown by the appearance and texture of the wet gluten prepared from the dried material. The results obtained for the rate of imbibition of the dried material with lactic acid show very clearly that the colloidal structure has been profoundly altered by the drying process, the most pronounced change being in the case of the strong flour gluten B It is of interest to note that drying causes the various glutens to become more alike in so far as ail colloidal properties are concerned.

The strong gluten in particular shows a lowered imbibitional capacity. This is what might be expected if the imbibitional capacity is due to marked colloidal properties, for we know that alternate freezing and thawing or subjection to altemate moist and dry conditions tends to break up the colloid complexes of a soil, and approximately the same factors are operating in the present instance. The object of this investigation was not to investigate differences between glutens before and after drying but to study the glutens from the strong and weak flours, which explains why the drying experiments were not carried farther.

The baking tests show that these flours are distinctly different. B is what is known as a strong flour and B and B as weak flours. Here again in the case of alkalies the "strong" flour gluten has a higher rate of imbibition than has the "weak" flour gluten. Indeed dispersion and imbibition are here ahnost coincident. When sodiam perborate is treated. Instead of hydrogen peroxide other oxidizing agents may be used, such as percarbonates or sodium peroxide. On the request of "Die chem. Pabrik Grunau," Berlin, Professor Kurt Arndt started some research work on the problem, and in he happened to observe that sodium perborate was formed when electrolyzing a solution of borax containing sodium carbonate.

A condensed report on tMswork may be found in the Zeitschrift fur Elektrochemie, By the electrolysis of a solution containing sodium carbonate and borax, sodium percarbonate is probably formed as an intermediate, which reacts instantaneously with borax forming perborate. By this process it is possible to produce sodium perborate directiy, doing away with peroxides of hydrogen and sodium.

The importance of this invention is obvious.

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Some years ago Trygne Valeur did some research work at the Institute of Technology of Norway, in connection with the electrolytic production of sodium perborate. At that time he did not know anything of the work of Kurt Arndt, and the.


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In spite of variation of working conditions, and use of different electrolytes the quantities of sodium perborate obtained were very small. What made the problem look rather hopeless was the tact that that on electrolyzing a solution containing some sodium perborate, this was decomposed, no matter whether a diaphragm was used or not. It thus appeared that on electrolyzing a solution of sodium perborate, this is decomposed anodically as well as cathodically. On the other hand, the solubility of borax is very small in cold water, and as it may be assumed that the current efficiency increases with increasing concentration of borax in the electrolyte, the first experiments were carried out with a solution of borax and sodium hydroxide.

On account of the greater solubility of the metaborate, such a solution can be made rather concentrated, even at a low temperature.. In order to increase the current efficiency a diaphragm was first used. As this causes the alkalinity of the anodic solution to decrease, the borax bas a tendency to crystallize if no precautions are taken. For this reason, from the beginning of the electrolysis, there was added an excess of sodium hydroxide and the electrolysis was run until the borax began to crystaUize out.

From the results thus obtained, we gain an idea of the influence of the alkalinity on the formation of the sodium perborate. It now appeared that the concentration of the sodium perborate always increased during the electrolysis, until the point where the crystallization of the borax sets in. From that moment it begins to decrease, although very slowly. TidssMft for kemi Farmaci og Tempi, Kristiania, This indicates that under the prevailing conditions the maximum concentration found is the largest obtainable at aU.

Since the sodium perborate is not only produced, but also decomposed at the anode, it seems very probable that there must be a concentration, at which the formation and the decomposition of the perborate counterbalance each other. The diaphragm used was a porous cylindrical clay cell, containing 85 ce of the anodic solution. The anode was a platinum sheet with a total surface of 6. The current was 1. The cathode consisted of an iron plate surrounding the diaphragm cell.

In order to keep down the temperature, the beaker was placed in ice water. The maximum concentration was reached after hours of electrolysis. It appears that the production of sodium perborate is increased essentially by inereasing the concentration of sodium carbonate in the electrolyte, whieh is only what might have been expected beforehand. Some experiments were then canied out with electrolytes corresponding to those in Table I, with an addition of smaH amounts of different substances.

Thus sodium fuoride was tried, which raises the overvoltage; also sodium phosphate, which is stated to stabilize perborate solutions, and many others. In most cases the addition had practically no effect upon the formation of the perborate, and in some they were detrimental.

Sodium silicate—water-glass—however, proved to be favorable, as is shown by the following three experiments. Except for the content of wa-ter-glass, the working conditions of these experiments were the same as in the experiments Nos. Table 1. This layer, however, became visible only at the end of the experiment. When electrolyzing a solution con-. There is therefore a marked difference between sodium carbonate and water-glass, as to their effect upon the formation of perborate.

This difference is aiso shown by the fact that the effect of the water-glass as contrasted with the sodium carbonate is independent of the quantity added within a wide range. In ait these experiments platinum has been used as an anode. It would, however, be of great interest, if the platinum could be replaced by a cheaper material. By the use of an anode of nickel, the maximum concentration bbtained corresponded to theamountof0. The next problem was to determine the effect of the eurrent density upon the maximum concentration of sodium perborate.

From the previous experiments it follows that the concentration of the sodium carbonate should be as high as possible, and for that reason, the electrolyte in ail cases was practically saturated with sodium carbonate. The working conditions were exactly as in the previous experiments. The results of these experiments are tabulated in Table III. When the electrolyte contains water-glass, the favorable current den. Besides the current density, there is another factor that might be of importance to the current eSciency, namely the temperature.

When determining the temperature most favorable to the electrolysis, it must be borne in mind that the. When varytag the temperature, it is therefore necessary also to vary the composition of the electrolyte, and to take care that the electrolyte is always practically saturated with sodium carbonate.

This is rather peculiar, as the solubility of sodium perborate in water is rather low. In order to get a more general idea as to the conditions of solubility, some experiments were made with very strong solutions of sodium perborate, prepared by means of hydrogen peroxide. By means of continuous analysis of the solution, the rate of crystallization could be followed, and the solubility determined in the different cases.

First it proved that the sodium perborate has a very marked ten- dency to form supersaturated solutions. UsuaUy crystaHiza-. Then it proved that sodium metaborate and sodium hydroxide increase the solubility of sodium perborate, while an addition of sodium carbonate causes some decrease in the solubility. The only thing to do in this case seems. In order to illustrate the state of things, when decreasing amounts of metaborate are in solution, the results of some experiments are given in Table V.

As mentioned before, it was impossible to induce crystallization of the sodium perborate in the experiments 9 and Contents per ce ofetMtrotyte Temper. As soon as it is possible to prepare solutions saturated or supersaturated with respect to sodium perborate, the most important question is no longer the maximum concentration but the current efficiency at that concentration of sodium perborate where the solution is saturated. When in the experiments 20 and 21, the amounts of sodium hydroxide are varied, the time required for the reaching of the maximum concentration varies also and hence the current em.

This is, however, stUl rather high and it proved more favorable to work with solutions containing no sodium hydroxide at ail, hence no metaborate. A further advantage is the possibility of doing away with the diaphragm. The tosses in current eniciency, due to cathodic reduction of tbe perborate increases, however, rather markedly with increasing concentration of the perborate. When therefore no diaphragm is used, the decrease in current efficiency is much greater, when the electrolyte contains sodium hydroxide, as compared with the cases where no sodium hydroxide is employed, and the concentration of sodium perborate therefore is much less.

The variation of the current efficiency in relation to the concentration of perborate may be seen from Table VI. CoateatspeflOOccof of t! The cathode consisted of two zigzag bent nickel wires, one on each side of the anode, of 1. As previously mentioned, it is also practicable, instead of sodium carbonate alone, to employ a mixture of sodium and potassium carbonates in the electrolytes. This makes it pos-. For the remainder of the experiment the working conditions were the same as those employed in experiment No. Also in this experiment an addition of water-glass proved favorable, when the amount was not too large.

In Table VIII are given the results of an experiment which differs from the above experiment only in so far as the electrolyte contained three drops of water-glass per ce. In order to have the sodium. In the following aregiven two experiments, carried out in a relatively large electrolytic cell, with a lower surface of em2l and containing 2. When the concentration of the saturated solution was reached, the solution was inoculated with crystals of sodium perborate.

Borax and sodium carbonate were added as they were consumed in the process. In the first experiment-using no waterglass-after crystallization had started and, equilibrium attained, the concentration remained between 1. The sodium perborate which crystallized out during the experiment, was carefully washed, dried, weighed and analyzed.

The current efficiency was calculated to be In the other experiment, using 2 ce of water-glass per liter of the electrolyte, equilibrium was established at an amount of As the contration of the saturated solution corresponds to the amount of about 1. These experiments, carried out by Valeur cleared.

For the technical and commercial utilization of the process, further important problems had to be solved, and the writer therefore, some years later, in the employment of O. Collett and Co.

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It will therefore be sufficient to refer to only one of these experiments, the results of which are shown graphically in Fig. The electrolyte had the following composition per liter:. By further electrolysis the concentration of the perborate remains constant, and equal amouhtsof perborate are formed and decomposed. When aUowed to stand, the content of perborate gradually decreased. On account of the spontaneous decomposition of the perborate, the beneficial effect of a greater volume is of course limited, as the decomposition is proportional to the volume of the clectrolyte employed.

It was impossible to prepare a solution wMch was absolutely stable, even at very low temperatures. Efforts were now made to purify tbe raw materials. It may be obtained from pure sodium carbonate by caustification with pure lime, or sodium carbonate may be used instead of sodium hydroxide, and the COs formed by the electrolysis removed by treatment of the electrolyte with pure lime.

A more favorable method was the caustification of the electrolyte by means of electrolysis. The electrolyte, whieh in this case was made purposely rich in sodium bicarbonate, was fed to the cathodic compartment of an electrolytic cell, canvas being used as a diaphragm, and electrolyzed until the greater part of the bicarbonates and carbonates of sodium was converted into sodium hydroxide.

Further experiments were therefore carried out in order to find another method for the removal of the excess of carbon dioxide. It had been observed that the carbon dioxide is partly liberated at the anode and thus removed from the electrolyte by the primary electrolytic process. As this fact. From time to time it is therefore necessary to replace the electrolyte partially by fresh solution.

The regeneration of the sodium carbonate and the borax from the old electrolyte does not oner any difficulties, as this is easily done by evaporation and crystallization. For these reasons it would be a great advantage to use an electrolyte containing borax and sodium carbonate only, and no potassium carbonate at ail.

The current efficiency certainly would diminish in this case, but at the same time the lesser solubility of the perborate in the electrolyte produces better conditions of crystallization. If the same relative area were to be used, when working on an industriat scale one ton per day , this would mean a surface of about an acre. This is of course impossible. In one of these experiments 1. Potassium carbonate was not used. When equilibrium was established the concentration of the perborate in solution corresponded to an amount of about 1.

Mechanical pbwef, power for cooling plant H. The amount of platinum required for this production is about 7 kg. In the preparation of selenium oxychloride. At or near the boiling point and under atmospheric pressures, the decompositions of selenium oxychloride which take place have been noted and are as Mlows2 SeOC! There is apparently a smaU amount of dissociation of the substance appearing as a factor at these temperatures. By reducing the pressure and thus distilling at a lower temperature these minor decompositions are very largely obviated. This consisted of a distillation chamber with a glass tube sealed on the top, the thennometer being hung to a ground glass stopper in the top of the tube.

The bulb of the thermometer was wound with glass wool which was tied on with the glass wool itself. The condensing flask was in turn connected to the vacuum system. The vacuum system consisted of three equaHzing bottles of twenty liters capacity each, a soda-lime tower and a U-tube manometer.

A partial vacuum was maintained by a large water pump. When the selenium oxychloride had started to distill, the temperature and pressure were read simultaneously. Observations were recorded in the modified RamsayYoung apparatus at pressures up to Above this pressure and temperature, it is considered that the method does not give sufficiently accurate results. Por the higher temperatures a distillation flask was used.

The flask was heated on a sand bath by means of an electric hot plate. The pressure was read direclly on a syphon barometer whieh was connected to the vacuum system. The mouth of the vessel was plastered with paper-pulp and the edges were smoothed by painting a thick paste of the soaps in suitable solvents.

It has been pointed out that a coating like this is liable to crack. It was found that pastes of most of the soaps in methylated spirit did invariably crack. The best soaps for this purpose were those which were gummy, and of a curd-1ike structure, and the best solvent was benzole. To this fact may also be attributed the inferiority of alcoholic solutions of these soaps for water-proofmg filter papers. FeMday Soc.. If a proper soap solution and a suitable kind of paper-pulp are selected the rather expensive method of making the paper fibre water-proof by giving a 'thin coating of the water-proofing material by a brush can be replaced by the adsorption process described here.

Considering the saving in material the results obtained are fairly enicient, and the defects of the crack-formation which are so ruinous to the efficiency of the basin as a water-proof utensil are also obviated in this process. It is shown that FreundHch's empirical ruie holds good in several cases. The methods of making water-proof basins have been brieny described. WoMd' has recently described experitnents in which he nitefedwater and other liquids through cohodion filters and in this way obtained liquids which showed no bright speeks under the ultra-microscope. In expressing these resalts, however, he uses language which is capable of a very dMerent interpfetation from that which is justiSed by his experiments.

In the exhausted apparatus, Fig. Absttaeta, a, A converging beam of sunlight, directed by a heliostat and passing through a ce! The flow of water through D was produced and controlled by a slight tilting of a board on which the whole apparatus, induding the microscope, was Mxed. If no dises passed the rate was taken from other experiments in whieh the board was given the same tilt. Wolski found 29, so it is evident that he and 1 are looking at the same thing.

The relative lightscattering of this water was 0. Martin itt bis apparatus described in Jour. Experiments to determine the actual scattering of water filtered through collodion afe m progress. Preliminary experiments in which the collodion film was formed on a fine b! It is hoped that Wolski's method of filtering will make it possible to extend the scope of the measurements of light-scattering to solutions of non-volatile substances to which the method of purification by distillation has not been applicable.

It was barder ta nase out the motes hom this apparatus thau fron Martin's p! A cross-shaped container Fig. Such a con- tainer had a small volume about 20 cc and when painted black on the outside permitted. Oceasionally after completion and without apparent cause a plate would crack. However a dozen or more such crosses have been successfuUy made and used.

It proved more difficult to make the crosses from sodagtass tubing. Evidently the glass of which the plates were made had a somewhat different coefficient of expansion from that of the tubing. FinaMy it was found that the crosses could be made quite easily from pyrex plates and tubing. It proved to be very easy to make the seals from such plates, even with no special annealing. The seals, when made with a dentist's blow-pipe burning gas with air. The liquids were rendered free of dust by the method of distillation described in the former paper Fig. Onty slight modifications were made in the apparatus for measuring thelight-scattering.

A "Pointolite" tungsten-arc lamp proved to be a very satisfactory point source and replaced the troublesome carbon arc. The exciting beam of light passing through the cross was wider than before, and the scattered light was observed through a slit about 0. The liquids used were Kahtbaum's and Baker's C. Benzene bas been chosen as the standard for comparison.

Kahlbaum's gold-label benzene for molecular weight determinations, and Baker's C. This did not, however, prove to be true for aU liquids. In Table I, Columns 1 and 3, are the results of the measurements of relative intensity and polarization of the scattered light for a few members of the benzene series, a few alcohols, and water. Similar measurements for some other pure liquids are given in the section on solutions. The results do not differ markedly from those given in our previous paper. The averages of various sets of readings Jouf.

Mquid B. Benzene M LOO Xyleae' Methyl alcohol? Ethylalcohol 78 0. Various formulae have been tried to find one which would best fit the experimental results. The values of. His equation contains a factor which is an expression of the extent of the polarization of the scattered light; but,.

See also Aan. His modified formula is. The two parts of the apparatus. On jarring the apparatus the spring released the hammer, which in tum broke the glass ball. A measured volume of the liquid in B could then be It is dMScutt to distill directly a liquid wbich has been previously made up to a known composition.

The more volatile component goes over Srst, and uatess the Mquid be completely distNed over, the composition of the distiihte in the cross is unhnown. Separate dtstiHations, moreover, must be made for each composition, whereas with the apparatus deseribed above as many compositions as desired may be studied after one set of distiHatioas. Generatly four distillations sufficed to wash the.

Pemutt by volume Ret. Rdative Scstterimr. This is surprising in view of the fact that the refractive index of such solutions is apparently an additive property. Liquids which polarize the scattered light very far from completely show, on dilution, much more nearly complete polarization. In Fig. This assumption would help to coUate the behavior of liquids with that of gases, for a comparison of our results for liquids with those of Strutt and Cabannes for gases shows that gases scatter more light, and also polarize the scattered light to a greater degree, than do the same substances in the liquid state.

Lord Rayleigh in formulated the relations for the light scattered by a nearly transparent medium consisting of particles much smaller than the wave-length of light and distributed at random. His theory leads to the following relation:. M the number of scattering. This value Cabannes'. Some freshly distiHed carbon bisulphide' used because it scatters retativety so much light was placed in a flat-walled cell and illuminated by a beam from a mercury vapour lamp.

The intensity of the scattered light from a column of this liquid 2. The line A was isolated as before by absorbing solutions. Next the light scattered by the same sample of carbon bisulphide in a cross was compared by the usual method with that scattered by a sample of dust-free ether in a cross. Strutt has compared with gaseous ether a sample of liquid ether freed of dust by shaking with water.

He found that such ether scattered one-seventh as much light as did the same amount of ether in the gaseous state. We find that a sample of ether shaken up with water scatters about 1. This would make dust-free ether It is hoped shortly to increase the accuracy of the above measurements, and to make similar measurements for other wave-lengths of light. Such measurements would put to a strict test the inverse fourth power law for liquids. SS, When the volume occupa by the motecutes is no longer very analt compared to the whole volume, the tact that two tnotecules caaaot occupy the same space detracts from the random character of the distribution.

And when, as! Fowle's reason for assuming that all the absorption was due to scattering was that the absorptioncoefficients for the various wave-lengths considered followed the inverse fourth power law. But this would also be true for scattering by fine dust particles. There is, moreover, no good reason to assume that the light of the shorter visible wave'iengths has no heating effect. It would be very interesting to study the light-scattering of some gases near the critical conditions. Strutt gives results for carbon dioxide at high pressures which indicate that for the pressures and temperatures at which he worked the scattering was proportional to the density of the gas.

If this be true some rather sudden departure from this relationship must occur at or near the critical point. The authors have in prospect the measurement of some extinction-coefficients for dust-free water and other liquids to obtain further evidence on this disputed question. The relative intensity and the polarization of the light scattered by various liquids have been measured with an accuracy greater than that attained in our previously published papers.

This increased accuracy was made possible by the use of cross-shaped containers with sealed-in, flat, glass endplates in place of the bulbs used heretofore. Measurements of the light scattered by two-component liquid solutions show that the relative intensity of the scattered light is always somewhat greater than that caleulated on the assumption that the scattered light is an additive property for the two liquids. Uqnids which polarize the scattered light very far from completely show, on dilution, amch more nearly complete polarization.

The results show that ether and w ater scatter about onetenth as much light as do the same weights of these liquids in the gaseous state. A comparison of these ratios for the three wave-lengths shows that the intensity of the scattered light varies inversely as the fourth power of the wave4ength. Chemtcat WatfMe. Fries and Clarence 7.

It is hoped thst the tacts here presented may further increase the interest ht Chemins! Warfare, for there is no question but that it must be recogaized as a permanent and very vital branch of the Army of every country. Reasons for this will be found scattered through the pages of tMa book. The result is what might bave been expected, an admirably writtea, weit-bataneed book wMch covers the ground thoroughly and ia au iaterestiag manner.

The reviewer bas been htterested to note that the book stnkes anay oCScers who are aot chemists just aB favorably as it does those who taow chemistry at 6rst hacd aad war oaly from books. It is to be hoped that this book wiM get the wide circulation that it deserves. Dundonald's proposa! Por the man in the trench or ahett hc!

N be used to stari battles, change fronts, order up reserves, and SnaMy to stop fighting. There ie a foot-note on p. This disturbiog factor is absent with black smoke. It is probable that the. There was one lesson which the war taught the Chemical Warfare Service and whieh should have been emphasized more strongly in the book. Imt was the need for more adequate co-operation between the home and the foreign services. Things cannot be handied adequatety by cabte or by letter. There ohoutd have been a constant stream of good omcers goiag from the United States to France and staymg there for a month or six weeks.

Untll Col. Thefe was obviously nothing of aoy value to be got out of young engineer officers no matter how capable they were. Coatempotary Science. Auld; What are Enzyme:? Sir Chartes Parsons states, p. The former may cornet of acid. Mtd be obtained if we! At 25' they Mve Humaa beings and most mammab differ ia tMs respect from im. Unfortunately ouf body does not to! A man may breathe quite comfortably in an atmosphere in which a candie is extinguished. The caod e is affected by the proportions of oxygen and nitrogen.

U2 he says that "it Js particuiariy iaterestiag to note that when the breathing test la pushed beyond the llmit that the man can endure, be it the equivalent of only 10, or 26, feet, two different physio! The other and better type, on the contrary, goes to the equivalent of a tremendous altitude on the rebreathing apparatus and ioses consciousness, beconung glassy-eyed and more or iess rigid, but without fainting. The former variety chances indeed to be in the minority, and hence it bas come about that the diseases to be successfutiy combated by antitoxins are few in number, while those in which the microbes penetrate deeply into the body and which poison its tissuesbytneaasofso-caUedendotoxin.

And yct the faiiures have been only partial and suceess bas been and is stiB being won against odds which were once considered insuperabie. Because of their size. And yet iamentabte instauoes. These have occurred especially in conaection with the therapeutic employment of curative serums. Thus it bas beenfound that when a sensitive anima! And thus human bcmgs who are sensitive. Keea gives some awfm agutres, p.

CM such amputations in hospitala, SSS died or 41 percent. Of m country practice, died or M. In the large Parisian hospitats CZ percent died after these amputations and 11 percent after amputations in isolated roonts in country practice. It appears, therefore, to be an interesting task to attempt to present the material commonly treated m elementary bocks on chemistry in a form which cowtd be reasonably wett fottowed by the student through private study and with the smallest amount of explanation on the part of the teacber.

No attempt has been made at condseness in the discussion of important ptinciples. Analogies have been repeatedly pointed out in an endeavor to indicate to the student the way in which he should ciassify the tacts brought to bis atten. The law of mobile equiiibrium. This is praiseworthy and the book M interesting reading to the chemist. It btinga up the oM question as to the proper order of trestment.

Perhaps the inductive, or so-taUed scientifie method is the best for the beginner, though it is admittedly not the quickest way of getting a knowledge of the subject. There is a story that Louis Agassiz was once asked whether he began his lectures with a statement of the fundamental laws and he answered that he began with a bushel of clams.

Norris has done the work he plamied in an admirable way. There are one or two slips but they are of relatively little importance. The expianatioa that nature abhors a vacuum was not put forward to account for the fact that water cannot be raised more than thirty-four feet by a suction pump, p. While it is true, p. There seems to be a surplusage of ciphers in the statement. The reviewer teamed something from the statement about long names, p.

The statement in regard to rusting, pp. Whether or not the metal is appreciably corroded is determined by the physical. Nickel, cobalt, and tin are anected to only a sHght degree if at att: zhc becomes covered with a thin coating of basic carbonate, which resbM further action and b, theretore. A cieaa surface of copper ox! The sca! Rust itself forms a couple with pure iton and when it is once formed the corrosion proceeds more rapidly. It bas heen shown that the rate of rusting during the secoad year is about twiee as fast as during the first year. When iron is straiaed in aay way it assumes a different potential from that of the uastrained metal, and, as a result corrosiom is greater in the aeighborhood of punched hales than around holes drilied in the metal.

Cofmsion takes place where the metal bas been scratched by a file or struck with a heavy tool.. Bancroft Organic Compoands of Mercury. By Frank C. It soon became evident that the work could aot be aU-inclusive. Atteatiom will therefore be confined entirely to the true organic mercury compounds in which mercury is attached direetiy to carbon. Another subject of considerabte interest wMch cannot be discussed tothehostof 'double compounds' ofmetOtrycompoands and organlc substances.

Hsts la the Appeadix. The subject h treated under tbe general heads: Mstorica! It mtght be thought that there would be little h! The formation of methyt tnercwic iodide ht sunlight p. Jones "advanted evidence to show that the two benzyl groups in mercury dtbenzy!

Gravity Visualized

This is im harmony with tbe fact that the mercury appears as the free metal at the end of the reaction. This deposit is a good conductor of eteetncity but does not amatgamate with mercury. H8, , The problem is of theoretical tather than immediate practica! Cases are known ia whtch this hydration takes place under the iaNttence of dilute add atone.

Such a case is that of ptpefonyt acelyteme whieh gives the eotrespondinx ketone on wanaiN: with ditute hydrochloric add. Hg OR X. Neither fonnuJa explains ail of the reactioas. Acids and alkyl ha! Vanoas teactions give formic acid derivatives, a fact which is hard to explain by the second formula. The same teagents give another ptoduct wh! In an. He ptaces the mercury compound in an iron crucible, covers it with a mixture of barium and sodium carbonates, and heats very gentiy.

Bancroft ConteatmtioB by Ptetatioa. Rickard beHeves, pp. That is the conclusion that mostseientMc men wHi reach, though it apparentiy cannot be proved iegaMy. What ls needed is a suf5cient! It happens to be easier to secure this with substances which lower the surface tension of water; but that does not affect the general theory.

Dureti says, p. A hypothesis based on nascent and ocduded gas explains aii kinds of Notation as well as notation machines. In the same article, p. DureM says "that an acid or any electrolyte creates osmotic pressure, by trying to enter the solid. If this pressure be suffident to drive most of the gas out from the gangue particles, the tnetaiHc partides can be Noated, for the reason that there is stiM ieft MuSdent gas in them to become nuclei for bubble formation by the nascent gas of the Mquid Everyone who bas experimented with ftotation bas seen how too much acid wiii 'MH' the Noat.

In maintainiag that osmotic pressure of an electrolyte is the cause of selective flotation, it is weU to look into the motive power of osmotis. However, ail theories of Notation, be they electrical or otherwise, must come to osmosis for their solution. There seems to be ao good reason to suppose that an electrolyte, as sueh. Bvea, then, it is not clear what itaportaatpartispiayedbyosmosh. It temains to be seen how Minerab Separation wH! Rickard also states bis bdief that "the validity of the patent for a soluble frothing agent should be fought to a finish and it shouid be ascertained what is a'soluble frothing agent' and whether tt is covered by the description of the oit ia the first patent.

The chapter on metallurgy takes up iron and steet. One does not see why the lead storage battery should corne in under metaNNrgy. The reviewer doubts the statement p. F , which is found in Greentand as the minerai cryoUte, gave mdted metaUie atumiamn. Gortaer, R. Re: 13, , Fix. W: On the cOXddat sweuing of wheat gluten. Upson, P. The problem therefore is a deeper ope than merely a study of the action of salts or acids on the physical properties of a colloid. It is a theorem in colloid chemistry that a colloidal system has a "memory," that the colloidal behavior of an emulsoid sol or an emulsoid gel is dependent not alone upon its present environment but upon its past history, and it would seem that the past history of the gluten while it is beiag deposited in the endosperm of the wheat berry is the detennining factor of a strong or of a weak nour.

Such papers as bear upon the subject under consideration will be considered from time to time as latep papers are prepared for publication. OstwaM, W. Uber koMoM. KoU Ze:t. ZurVbkosimetde der Mehle. MeM, H. LOen, H. Beitrage zur KoNoidchemie des Bfotes. These workers make no mention of the work by Gortner and Doherty and they, like Upson and Calvin, reason from analogy rather than from actual experiments made upon both strong and weak t[ours.

For example, Cohn and Henderson'" state, "The 'body' of the dough is supplied by the wheat gluten alone. The degree to which the dough can be distended therefore depends upon the amount and the hydration of the gluten. It is impossible to determine from the data given in the papers of Henderson, et al. The physical chemistry of bread making. Sdence, 48, H: On the control of rope in bread. Hendersoa, L. H-, WachnMN, J. Unfortunately no nitrogen detenninations are available, nor is the source or grade of the samples noted.

He finds for the flours which he investigated that "flours with high gas-retaining capacities and high bakers' marks have been shown to be those in which the 'amended gliadin' figure is high. It would be interesting to know whether or not the proteolytic enzyme activity MfMd with the different flours which Martin used. In one of the flours which he worked with he showed that there was appreciable proteolytic activity. He a1so pointed out that the diastatic activity varied with the If Martin, P.

Unfortunately none of the flours with which Gortner and Doherty worked were available for the present series of investigations. Consequently it became necessary to repeat at least a part of their work using gluten from new samples of flours in order that the comparative data for the present set of flours would be complete. Imbibition in the presence of different strengths of the following alkalies: potassium hydroxide, sodium hydroxide, calcium hydroxide, barium hydroxide and ammonium hydroxide.

Theoptimum hydrogea ion concentration for the swelling of dises in. B is a first clear flour made in the same. B 0. It was thought advisable to repeat the bakings with flours B and B and also inasmuch as a low volume might be due to deficiency of soluble carbohydrates to investigate the effect of diastase.

Jessen-Hansea'" has pointed out that the optimum hydrogen ion concentration for baking is around pH value of 5. Comptes-rendus des Travaux Lab. Itisregrettedthatthesupplyoffioursdid not permit fufther tests along this Une, but the tests tend to show the superiority of flour B H: A metttod for the determination of the strength and baking quaUtiesof wheat NoNr.

Potass1um Sulfate-Soluble Protein. Two 50 ce aliquots were taken and protein determined as above. The material was filtered and the protein content determined as above. At the end of this time the material was filtered and nitrogen determined on aliquots of the filtrate. The residue remaining was then treated with a fresh portion of potassium sulfate solution and the process repeated.

This extraction was continued until six separate portions of potassium sulfate solution had been used or a total of about ce. Protein was determined on the total alcohol extract by the Kjeldahl method as described above. These determinations were ail carried out in duplicate. The average of the different determinations is given in Table III.

More dimculty was evidenced in collecting the gluten from B; it was rather intermediate between B and B and B They were whiter, it was harder. Protem obtained by N X 5. F our Ptouf. It is particularly interesting to compare the data for B and B, the "strongest" and the "weakest" samples studied. The ash values are not widely different and are indicative of a "patent" and a "straight" flour. The crude protein values are almost identical so that, in this instance at least, the "weakness" of B does not lie in a lower gluten content. The marked contrast in the baking tests shows that in these contrasting samples we have excellent material for testing as to whether or not the differences observed in the baking tests are paralleled by differences in the physicochemical behavior of the glutens.

The Preparation of Dried G'M. Using dried material. Therefore the attempt was made to prepare considerable quantities of the dried glutens washed from the four flours. Consequently the drying must necessarily be carried out at a temperature that would not be at a11 unfavorable to bacterial and enzyme action. About 3 kilos of flour were made into a stiff dough with distilled water and allowed to stand under distilled water for an hour. The material was then placed in an electrically driven dough-mixing machine. Distilled water under considerable pressure was run continuously into the mixer at a rather rapid rate.

At the end of about 7 minutes atl of the starch appeared to have been removed, the liquid from then on remaining only slightly turbid; the treatment was continued for 13 minutes longer, the water by this time had begun to froth slightly. Glass plates were used for shelves in the vacuum oven and these little squares were placed on the glass plates at least 1 centimeter apart. It was possible to dry the material to a crisp in less than 18 hours by this method, the drying was, however, continued for a total of 48 hours.

This material showed no evidence of decomposition that could be detected by odor. The percentages of moisture and crude pro- tein are reeorded in Table IV. Lab no Mobtwe. Crudeprotein ia. From their data it is evident that two types of results may be expected, i. We have felt that it would not be profitable to repeat. The dises of gluten were al-. KOM Yt.

Imbibition Penod 50 Minutes. Average of 5 Determinations. Conceutratiou B B B B of acid. The Imbibition curves for the various gtuteas in different concentra-. It will be observed that there is a wide difference in the imbibitional capacity of glutens B Twenty grams of the dried gluten. Imbibition Period 50 Minutes. The top curve fs B.

Imbibition Pencd 25 Minutes. Average of 5 Detenninations. Concentmttott —————————————— —————— of acid Before After Before Befofe dfyiag dtyimg drying drying. SOt 0. It is of interest to note that in the 50 minute experiments B' has decreased in its imbibing capacity in lactic acid to a very appreciable extent, that. B has decreased somewhat but the other two glutens have not changed to so marked a degree.

This appears to indicate that the glutens are tending to become alike. In ail of the glutens the concentration of add necessary to produce maximum imbibition has likewise increased. It bas been our experience that weak glutens reach their point of maximum imbibition only in a higher concentration of acids than do strong glutens, and in the present instance the drying process appears to have produced a "weak" gluten as measured by rate and extent of imbibition. A series of sodium hydroxide solutions was prepared of the same normalifies as those employed m the study of the acids.

It was impossible to remove the dises at the end of the imbibitional period, ail coherence having been destroyed. In the case of the more dilute alkaline solutions the discs were coherent enough to be removed for weighing. In order to ascertain whether or not this was a case of complete. This showed conclusively that the gluten was in reality being dispersed and by the amount of precipitate one would conctude that the process was going on rather rapidly.

It woutd seem that the action of alkalies on gluten is somewhat different from the action of the acids. In the case of acids the first step is the swelling of the gluten with no apparent dispersion. In no instance was there more than a slight turbidity produced. In the case of acid there is marked imbibition as shown by appearance and by the increase in weight. In the case of alkali however the two steps, imbibition and dispersion, follow one another almost immediately so that in some concentrations they compensate each other. In the more dilute solutions the imbibitional factor is the more prominent, in the more concentrated solutions the dispersion factor is the most apparent.

No appreciable imbibition was noted however. In an attempt to make the imbibition factor more prominent the time for the swelling determination in the presence of alkalies was shortened from 50 minutes to 25 minutes. A comparison of the results obtained in these two time intervals is shown in Table XI. It was concluded from Table XI and the swelling size as shown by appearance that 25 minutes would indicate the imbibition factor more accurate! The imbibition of the different glutens was studied in so. Avefage of 10 Detenainations.

ConceatMtioaofatkaU 60 minutes zs miaMtes. Gluten for the Vatious Glutens before dfying io Different Con-. Imbibition period 25 Minutes. In the higher concentrations the dispersion factor is more prominent as shown by the fall in the curve. B and B behaved in ail respects like gluten B with the exception that the dispersion was more marked in the case of B and B Thts and is shown very clearly in Fig.

This dough was aUowed to stand under distilled water for one hour and was then washed in a stream of distilled water. As soon as the washing was begun, however, the gluten began to disperse. This was tried repeatedly with the dried glutens from the different flours. It was found, however, that if a very small amount of sodium chloride was added to the wash water the gluten immediately came together in a coherent mass whieh showed greater elasticity than the gluten before drying. It left open the question of why some electrons were in the nucleus, while others orbited at comparatively large distances.

Rutherford understood these objections, but gave priority to the experimental observation rather than electromagnetic theory. It was assumed that further experiments would explain these apparent anomalies. Bohr placed non—classical quantum constraints on the motion of bound electrons, leading to a definite set of allowed orbits, each with a definite total energy, the outer orbits having higher energies than the inner ones.

When an electron was in such an orbit, Bohr further asserted that no radiation would be emitted; radiation was produced when an electron made a transition from a higher orbit to a lower one. With the electrons in their lowest possible orbits, no radiation could be produced so the stability problem was avoided, albeit at the cost of an artificial and unexplained assumption. The Bohr model was certainly seen as a major advance, largely because it was able to explain many experimental facts, including the wavelengths of the spectral lines emitted by a hydrogen atom.

In spite of these successes, however, the Bohr model is no longer taken seriously. It is sometimes used figuratively, as a sort of cartoon, but the modern theory of atoms is based on a far more fundamental revision of classical ideas. The final theoretical step toward our current model of the atom was taken between — The final piece of the puzzle was put into place when Born i arrived at a probability interpretation of the wavefunction.

The complete theory made possible by these advances is now known as non-relativistic quantum mechanics. The final experimental step was the discovery of the neutron by Chadwick i in , although he was reluctant to identify it as a new elementary particle. This then allowed the theorists to dispense with the messy and ad hoc collection of protons and electrons in the nucleus.

The electrons have neither definite positions nor definite velocities, but it is possible for an electron to have a definite total energy and definite angular momentum magnitude. The quantum picture of an atom replaces the allowed Bohr orbits by allowed quantum states. The quantum states are characterized by discrete, definite values for the energy and angular momentum, but have rather fuzzy locations and velocities for the electrons.

As an echo of the Bohr model, the quantum states of higher total energy tend to spread out further from the nucleus. For this reason, the most energetic electrons in an atom are said to form the outer shell while electrons in states of lower energy occupy inner shells. A chemical element is uniquely characterized by the number of protons in the nucleus known as the atomic number , Z , which in turn determines the total number of electrons.

Modern theories show that the chemical behaviour is determined almost entirely by the number of the electrons surrounding the atomic nucleus and the quantum states they occupy. Each chemical element can however be represented by more than one nucleus; nuclear stability allows for the presence of a variable number of neutrons in the nucleus, which affects the atomic mass without significantly changing the chemical properties.

Nuclei which have the same number of protons, but differing number of neutrons, are known as isotopes. Therefore the relative atomic mass of different isotopes will be different as well. The detailed understanding of the structure of complicated atoms and molecules and their interactions requires calculations using quantum mechanics, but these are in general too difficult to be carried out exactly for any but the simplest cases.

Instead, it is customary to fall back on modelling these complicated interactions as traditional forces that have some form of distance dependence and depend on some phenomenological parameters. We will discuss these further in the next subsection. Study comment The concepts in this section involve some rather advanced ideas, some of which are covered more fully in other parts of FLAP.

Figure 6 Typical variation of a the interatomic force and b the corresponding potential energy for two atoms separated by a distance r. When the atoms are very close together there is a repulsive force as at point E , when they are further apart the force is attractive as at B. The types of bonding between atoms and molecules that are responsible for the properties of matter are ultimately based on quantum mechanics as well as electrostatic forces. The electrostatic forces primarily act between the electron clouds of the outer shells of the atom known as the valence electrons , and depend on the detailed spatial distribution of the electron densities.

In addition to the classical electrostatic force, there are important restrictions on the quantum states that electrons are allowed to occupy, through the mechanism known as the Pauli exclusion principle. Under some circumstances, the exclusion principle places restrictions on how particles can move, in the same way that classical forces in physics affect the way particles move.

This effect can be pictured as a new, non—classical repulsive force called the quantum exchange force. Thus, the Pauli exclusion principle leads to an effective repulsive force between electrons, and hence between atoms. It is the combination of this quantum force with the electrostatic force which is responsible for atomic interactions. A typical form of the force between two atoms is shown in Figure 6. The essential characteristics of this force are that at large distances it is attractive, tending to pull atoms together, while at small distances it is repulsive, tending to push them apart.

The detailed understanding of these bonds requires a deep understanding of these topics, which are studied in somewhat more detail elsewhere in FLAP. Here we will pursue only a qualitative understanding of these forces, which will help us to understand the varieties of matter and its phases.

Figure 7 A model for ionic bonding between atoms, illustrating the positive and negative ions bound by the electrostatic force between them. Figure 8 An illustration of covalent bonding between atoms, the result of sharing of electrons between two atoms. In all cases, the length scales of the interactions can be inferred from our experimental knowledge of the spacing of atoms in physical systems. By directionality, we mean that the exact form of the force curve between the atoms or molecules will vary depending on the angle at which they approach each other.

Pure ionic bonding illustrated in Figure 7 involves atoms which actually transfer one or more electrons from one to the other, forming a pair of positive and negative ions. These can then be pictured as interacting through the classical electrostatic force. Covalent bonding involves the sharing of electrons between atoms, and can be pictured as a state in which the electronic density is higher between the two atoms involved shown schematically in Figure 8 than would be the case if they were treated as isolated spheres.

The cores are positive and are attracted to the electron cloud, which provides the effective force between the atoms. Metallic bonding only properly occurs in condensed systems with many atoms, and represents a sharing out of electrons into a sea of conducting electrons that belong to no individual nuclei. It can be regarded in a sense as a limiting case of the covalent bond, is non-directional, and has a typical magnitude of 0. The hydrogen atom has only one electron, so it can only form one bond in the usual sense.

However, the hydrogen atom is unique in that the positive ion is a bare proton, which allows other atoms to reside very close to it. When a hydrogen atom bonds covalently to another atom such as oxygen, for instance , the shared electron tends to have a higher probability to be located between the two atoms participating in the covalent bond. This leaves the hydrogen atom appearing as an electric dipole i to a third atom, which can form a weak bond with it.

An electric dipole can be regarded as a sort of dumbbell of equal positive and negative charge separated by some distance. The system will be electrically neutral overall, but can still interact electrically with other electrical systems. A fluctuating dipole is produced by time—dependent variations in the shape of the electron cloud of an atom. This dipole creates an electric field which induces a dipole in neighbouring atoms.

It is the interaction between these fluctuating induced dipoles that produces a small attractive force between atoms. Because of the overall electrical balance, the energy of van der Waals bonds tends to be substantially lower, on the order of 0. They also tend to be fairly non-directional. Note that all the types of bonding mentioned above are simply categories which are not totally distinct, but represent idealized models. In real systems, these different effects merge into a continuum of bonding behaviour, with particular systems being closer to one model rather than another.

Study comment We will present concepts in this section that are elaborated in other modules in this block. You will be familiar with the three ordinary phases of matter , by which we mean the forms that matter takes, each of which has its own distinctive properties. These three normal phases are gas, liquid and solid, and are exemplified by our everyday experience with steam, liquid water, and ice. We now want to characterize the macroscopic differences between these phases more carefully, and try to understand what they imply about the microscopic states of matter in these phases.

In everyday experience, a gas is characterized by low density, fluidity, and the fact that it fills any container, adopting both the shape and volume of the container Figure 9. It is also true that, for normal temperatures and pressures, a gas is rather easily compressed. A liquid is also a fluid, but typically has a much higher density than a gas. It still adopts the shape of its container, but the most significant difference is that the liquid has a definite volume, and resists compression more strongly.

Finally, a solid has a somewhat higher density, but is essentially distinguished by its rigidity, so that it tends to maintain both a definite volume and a definite shape. It must be admitted that these distinctions between the different phases of matter are not always clear-cut. A gas can be pressurized and made more dense so that it becomes viscous, like a liquid.

Solids can sometimes flow very slowly, as you can see from the distorted shapes of some very old stained glass windows. Nevertheless, the distinction between gases, liquids and solids is usually obvious enough, especially when there are clear transitions from one phase to another, as when ice melts or water boils. In approaching the understanding of these different phases of matter, it is important to remember the modern point of view that all three consist of the same basic atoms or molecules.

This is made more plausible when we recall that the three phases can be transformed into each other by appropriate changes in their temperature or pressure. We want to understand the phases in terms of a balance between the forces that act between the atoms based qualitatively on the typical force curve in Figure 7 and their kinetic energies. As the temperature of a substance is raised, so the average kinetic energy of its atoms or molecules increases.

It is no accident that solids form at low temperature, liquids at higher temperature and gases at higher temperatures still; the increase in temperature corresponds to giving the atoms in the substance more kinetic energy, allowing them progressively to escape from the confining attraction of the interatomic forces. Let us start with the gas phase which is found at high temperatures.

This has the lowest density, which implies that the atoms are farthest apart from each other. In terms of our force curve, this means that the force experienced on average is a small attractive force, but generally so small that we can treat the atoms as having no force acting between them most of the time.

Only very occasionally do atoms come close enough together to experience a strong repulsion; they then collide rather like billiard balls, exactly as assumed in the classical kinetic theory of gases. Ignoring the small effects of gravity, the molecules in a gas can be thought of as undergoing high—speed straight—line motions, punctuated by random collisions with other molecules and collisions with the walls of the container. A liquid can be produced by cooling a gas. The reduction in temperature corresponds to a reduction in kinetic energy of the atoms or molecules, until there comes a point where colliding molecules do not necessarily separate after a collision; for technical reasons related to conservation laws this requires collisions between more than two molecules, but once the condensation process has started it gains pace and a liquid phase is rapidly formed.

A second way of producing a liquid from a gas is by compression. As one compresses the gas the average distance between the molecules gets smaller, until the distance is such that on average, the molecules are in the region of the force curve corresponding to strong attractive forces. If the temperature is not too high, the gas will then liquefy.

Over a short interval of time, a typical molecule in the liquid agitates to and fro, as if trapped in a cage formed by its nearest neighbours but, every so often, a molecule escapes and moves to a different part of the liquid. The overall picture is reminiscent of a barn dance in which partners occasionally change group; it is this freedom of molecules to change their neighbours that allows the liquid to flow.

Going from the liquid phase to the solid phase , we are primarily removing energy, so that the average speed of the atoms is lower. This means that their motion and position is more tightly constrained by the equilibrium position of the force curve. In a solid the individual atoms oscillate about fixed equilibrium positions, and there is only very limited scope for motion through the solid diffusion. In a crystalline solid the atoms are tightly regimented into a regular array, quite unlike the more random assemblies in gases, liquids or amorphous solids.

Remember, it was the existence of such regular arrangements of atoms that produced sharp spots in an X—ray diffraction pattern and gave good evidence for the existence of atoms in the first place. Finally, we can schematically represent these three physical states at the atomic level as in Figure From these data, calculate how many carbon dioxide molecules there are per cubic metre in the three phases. We now need to multiply this value by the density in the three phases to obtain the number of molecules per cubic metre for each phase.

This calculation gives 1. The concept of atoms has been in existence in one form or another for more than two thousand years, at least since the time of Leucippus and Democritus in the 5th century BC, but for most of that period it had only philosophical significance by modern standards of scientific theories. Atoms only became a detailed basis for theories of chemistry and physics in the 19th century.

Under the lead of Proust, Dalton, Prout, and Avogadro, the idea of atoms as the elementary constituents of elements and of their combination into molecules to form the constituents of compounds led to the understanding of experimental results in chemistry. Physicists such as Daniel Bernoulli, Clausius, Maxwell and Boltzmann developed the kinetic theory of matter, which allowed for the first time the detailed calculation of macroscopic properties of matter on the basis of the behaviour of microscopic entities. The phenomenon of Brownian motion in the 19th century provided the earliest experimental evidence for the existence of atoms, although it required theoretical substantiation in the 20th century to be finally convincing as a manifestation of the random impacts of submicroscopic particles in the fluid.

Modern electron and field ion microscopes produce direct images of the surfaces of solids at the atomic level, but the most detail is furnished by the recent developments of scanning tunnelling microscopes and atomic force microscopes , which allow detailed pictures of surfaces to be obtained with resolutions of less than a nanometre.

These can also be used for manipulation at the atomic level, allowing for the ultimate in control of structures. The forces that bind atoms and molecules are the classical electrostatic force combined with the non—classical quantum exchange force, a consequence of the Pauli exclusion principle. Although the binding can only properly be understood in terms of detailed quantum—mechanical calculations, these are too difficult and complex to allow for easy understanding, and it is customary to model the behaviour in terms of different types of bonds.

These range from the ionic bond , which has almost completely localized electrons, through covalent bonds , which have valence electrons shared by atoms, to metallic bonds , which have the valence electrons almost completely delocalized, being shared out among all the atoms in the solid. Hydrogen bonds and van der Waals bonds are weaker mechanisms which come into importance only when the stronger bonding mechanisms are absent. The standard three phases of matter are the gas, liquid and solid. At the macroscopic level, these differ in their density and rigidity.

At the atomic level, these phases can be understood in terms of the balance between atomic and molecular separations and forces and the energy available to the constituent particles. Describe the fundamental ideas about the existence of atoms and relate them to chemical and physical principles. Give the magnitude of the size of atoms, and discuss the experimental evidence that provides these estimates.

Discuss qualitatively the various forms of bonding between atoms, and the relationship between these bonding forces and the different macroscopic forms of matter. Study comment You may now wish to take the following Exit test for this module which tests these Achievements.

Basic Concepts in Physics | SpringerLink

If you prefer to study the module further before taking this test then return to the top Module contents to review some of the topics. Study comment Having completed this module, you should be able to answer the following questions each of which tests one or more of the Achievements. The proportion by mass or weight of each element in the compound is then just. Thus these proportions are fixed, or definite.

Reread Subsection 2. A chemist reports that 1. Do you think the result is likely to be accurate? Explain your reasoning. The ratio of these two quantities is 2. An experiment in X—ray diffraction using a wavelength of 0. Reread Subsection 3. Suppose a microscope were designed to use hydrogen ions i. The proton has a mass of 1. Assuming the protons and electrons were accelerated to the same speed, what improvement in resolution for the microscope would you expect? Since the quantum mechanical wavelength depends inversely on the mass, a larger mass implies a smaller wavelength. All other factors being the same, we would expect the improvement in resolution to be equal to the ratio of the masses.