CHEMICAL NEWS Nov

THE FOUNDATIONS
OF CHEMICAL THEORY

An Introductory Textbook. By R. M. CAVEN, D.Sc. (London), F.I.C., Professor of Inorganic and Ana lytical Chemistry in the Royal Technical College, Glasgow. Royal 8vo. Price 12s. 6d. net.

A concise account is given in this book of the foundations on which the structure of modern chemistry is reared. The story is simply told with the essential technique. The book meets the needs of degree students in chemistry, who require a book introductory to the larger treatises on physical chemistry.

SCIENCE AND THEOLOGY THEIR COMMON AIMS AND METHODS By F. W. WESTAWAY. Royal 8vo. Price 15s. net. "This book travels through wide spheres of human knowledge in philosophy, science, and religion. There are, indeed, few branches of science which Mr. Westaway does not touch upon; and he successfully maintains throughout the work a high standard of accuracy and interest. As a survey of the main results of modern science it is admirable. Mr. Westaway is an able and lucid writer."--New Statesman.

ELECTRICITY

AND ITS PRACTICAL APPLICATIONS A Textbook of Electrical Engineering. By MAGNUS MACLEAN, D.Sc., Professor of Electrical Engineering, Royal Technical College, Glasgow. Fully illustrated. Demy 8vo, price 12s. 6d.

This book is designed to cover the subjects treated in a first-year course of Electrical Engineering. Special care has been taken to explain clearly the physical facts which underlie the action of all electrical machinery and appliances.

Ease in calculating electrical quantities must be acquired by every electrical engineer, no matter what special branch he may take up, and to make the path as easy as possible for the student, a large number of worked examples and exercises, with answers, are given, and a special Appendix has been written explaining the Electrical Units employed in Engineering.

APPLIED OPTICS

THE COMPUTATION OF OPTICAL

SYSTEMS

Translated from the German of STEINHEIL and VOGT. BY JAMES WEIR FRENCH, B.Sc. In Two Volumes. F'cap quarto. Price 30s. net.

"... Mr. French has provided an excellent handbook, which we commend to the serious attention of every student of technical optics."-Philosophical Magazine.

ITS PHILOSOPHY AND ITS PRACTICE By F. W. WESTAWAY. New Edition. Demy 8vo Price 10s. 6d. net.

"Mr. Westaway has a singularly acute and active mind which has engaged itself with almost all branches of human study; and he has the rarest of all gifts among Englishspeaking philosophers, that of directness and lucidity of style. The problems of metaphysics; probability and causation; the higher principles of physics; space, time, and infinity; the origin of the earth, and of the universe; the evolution of the animal species, and of man; life's consciousness; instinct and intuition, all these are treated with an assured knowledge, a candour, and a lucidity which will, we think, have a real fascination for any intelligent inquirer."-Times.

TIDAL LANDS

A STUDY OF SHORE PROBLEMS By ALFRED E. CAREY, M.Inst.C.E., Fellow of the Royal Geographical, Geological, and Chemical Societies, and F. W.OLIVER, F.R.S., Quain Professor of Botany in University College, London. Copiously illustrated with 29 full-page plates in addition to figures in the text. Demy 8vo. Price 15s. net.

To the engineer, the subjects discussed in this work are of the greatest possible importance, and whether he may be interested in the facts here recorded from the point of view of river control. or of the reclamation of the foreshore, or of the arrest of sand-dunes, he will find much matter for serious thought and consideration, and many details likely to aid him in his undertaking."-Times Engineering Supplement. LIFE AND ITS MAINTENANCE

A SYMPOSIUM ON BIOLOGICAL
PROBLEMS OF THE DAY

The contributors include: W. M. Bayliss, F. G. Hopkins, E. Margaret Hume, A. R. Cushny, K. J. J. Mackenzie, E. J. Russell, R. G. Stapledon, A. S. Horne, Sydney J. Hickson, A. G. Tansley, Lt. Col. Martin Flack, R. C. M'Lean, F. W. Oliver, H. M. Vernon, Henry Kenwood. Price 5s. net.

"One of the most interesting books of the year," -Spectator.

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The manufacture of chemical glassware was unknown in this country prior to the war, but was undertaken by several glass makers at the express desire of the Government. I doubt very much if at that time they quite realised the immense task they had undertaken, or the difficulties they would have to overcome. It must be remembered that there were very few manufacturers in this country with any knowledge of this particular branch of the glass industry, and little or no skilled labour was available. It was an extremely difficult task to attempt. However, after nearly six years of experimental and research work, involving a large expenditure of capital, the British manufacturers have succeeded in producing laboratory ware equal, and in some cases, superior in quality to the best known German makes.

In the early days of the war promises were very freely made that some assistance would be given to manufacturers in order that the industry would be kept in Great Britain, and that the country should not again be dependent upon foreign countries for supplies of glass so vital to the progress of industries and to the defence of the nation. This is very briefly the history of the industry up to the end of the war. We have succeeded in our task and have proved in yet another instance that to chemical glassware the label "it can only be well done in Germany" has been falsely applied.

In spite of all the work done to keep this industry in the country, manufacturers are viewing the future with great consternation. Germany is making a very desperate endeavour to regain her control of this important market, and helped as she is by the existing rate of exchange and other causes, hopes very shortly to encompass the death of the industry in this country. The position is a very serious one, not only from the point of view of the manufacturers, but also of the nation at large. I do not know of a single industry which can successfully continue without labora tory ware. This manufacture is essentially a "key" industry, and as such should be kept in the country.

Early in the war the country was in a very dangerous position owing to the lack of supplies of glass, and steel manufacturers stated that they could no longer continue the production of steel for guns unless they were given immediate supplies of glass. Whether it was by mere accident or the deliberate design of Germany, we perhaps shall never know, but very shortly after the outbreak of hostilities, it was discovered that stocks

of chemical glassware in this country, usually very considerable, were extremely low. It is obvious that this condition of affairs should never be allowed to re-occur; yet what is happening at present? Germany is flooding the country with the glass apparatus, in many cases at less than the cost of manufacture of the actual glass from which the apparatus is made here. An example of this came to my notice a few days ago, the articles in question were German test tubes which were offered at 2s. 7d. per gross. The cost of the glass tubing alone from which these test tubes are made in this country, is, in this country, 6s. 8d. per gross. So long as the rate of exchange stands as it is at present, Germany will be able to continue competition under these unfair conditions against British manufacturers. The price is cheaper, and many consumers in this country continue to buy foreign-made glass simply because it is less costly. Were the German exchange today normal, the price of their glass would be extremely high. This is a very important point; sooner or later the mark will again become more or less normal, and there will be no limit to the prices which they will be able to charge for their glass, because unless some assistance is given to prevent the manufacture of these goods being forced out of the country there will be absolutely no competition against Germany, therefore, no limit to the prices she may extort.

I do not deny for one moment that in the earlier days of the industry much inferior glass was produced. This was only to be expected, and does not surprise those who were connected with the industry, but that period is now passed for ever.

I earnestly appeal to your readers, the majority of whom are interested in chemical glassware, to insist on being supplied with British-made glass, but it must be branded with the mark or name of the maker. There is a quantity of unmarked glass still being offered, the origin and quality of which is doubtful.

The Government is being strongly urged to provide protection for this industry for a period of years to enable it to be placed on a satisfactory basis, when it will be in a position to meet any competition that may come from the Continent. In the meantime it is essential that users give their support to this important home industry.— I am, &c.,

T. LESTER SWAIN.

THE PHYSICS AND CHEMISTRY OF COLLOIDS AND THEIR BEARING ON INDUSTRIAL QUESTIONS.*

SOME OBSERVATIONS ON PEPTISATION AND
PRECIPITATION,

By N. G. CHATTERJI and N. R. DHAR.

IN his article on peptisation and precipitation, Bancroft (second B.A. Report on Colloid Chemistry, 1918, p. 2) enumerates a large number of cases of peptisation. We have reinvestigated some of these reactions and come to the conclusion that in several cases the observations are not accurate. Thus we have found that silver chloride, silver chromate, and calcium silicate are not peptised in presence of a concentrated solution of cane sugar. *A General Discussion before the Faraday Society and the Physical Society of London, October 25, 1920.

What actually takes place is that, in presence of a concentrated solution of cane sugar or glycerin, the precipitate does not come down immediately. It only does so on keeping for some time. But if it is centrifuged and specially a little diluted, the precipitate settles down at once. It therefore appears doubtful that peptisation at all takes place in these cases. True peptisation cannot give any precipitate when centrifuged in this way.

We have been successful in bringing about peptisation of a large number of hydroxides by means of glycerin, concentrated solutions of cane sugar or grape sugar. Thus the hydroxides of iron, nickel, thorium, mercury, cobalt, &c., have all been peptised by adding a caustic alkali to the solutions of salts of these metals in presence of glycerin or sugar. In the case of uranium and gold, ammonium hydroxide should be used instead of caustic soda. In none of these cases any trace of sedimentation could be observed even after vigorous centrifuging. One curious fact in this connection seems to have remained unnoticed. It is generally recognised that a substance which can peptise another during the formation of the latter may not be able to do so when once the substance has been formed. We have now observed that not only is the above true, but that petisation can only be brought about if the alkali hydroxide is added to the mixture of the salt solution and glycerin. On the other hand, precipitation at once takes place if the solution of the salt is added to the mixture of glycerin and alkali hydroxide. Peptisation does not seem to take place in the case antimony hydroxide, copper fluoride, or barium sulphate.

A reference to the literature on the subject of peptisation shows the confusion that exists in this branch of chemistry. The nature of the solutions obtained by dissolving aluminium hydroxide, for example, in alkali hydroxides has been the subject of much discussion. The literature on the subject puts forth evidence in support of both the peptisation and chemical combination views. We have tried to solve the problem systematically by finding out whether any change in electrical conductivity of a solution of caustic alkali takes place when any of the hydroxides is dissolved in it. Incidentally, we have investigated the solubility of the hydroxides of copper, zinc, and cadmium in ammonia. We have found that a great increase in the conductivity of the ammonia solution takes place on dissolving these hydroxides. In this connection, it is interesting to observe that the cobalt-ammonium bases and the chromiumammonium bases obtained by the double decomposition of a chloride of cobaltammine or chromiumammine by silver hydroxide are fairly strong bases (Cf. Dhar Proc. Akad Vetensk. Amsterdam, 1920).

In the case of the action between sodium hydroxide and the hydroxide of copper, chromium, lead, zinc, aluminium, mercury, the following results are obtained. The conductivity of a solution of caustic soda did not appreciably change on the addition of hydroxides of chromium, aluminium, lead, mercury, whilst in the case of zinc the resistance of the caustic alkali solution appreciably increased when zinc hydroxide was dissolved in it. Hence we can conclude that the solutions of aluminium hydroxide, chromium hydroxide, lead hydroxide, mercury hydroxide, and copper hydroxide are cases of true peptisation

and not of chemical combination. On the other hand, in the case of zinc hydroxide, we get more of chemical combination than of peptisation. Or, in other words, the major part of the hydroxides of aluminium, chromium, copper, lead, and mercury exists in sodium hydroxide solution as a colloid, whilst the major part of zinc hydroxide remains as a zincate.

Bentley and Rose (Jour. Amer. Chem. Soc., 1913, XXXV., 1490), from their experiments, were led to the conclusion that freshly prepared aluminium hydroxide dissolves in dilute acetic acid to form a colloidal solution. If this be true, our conductivity experiments ought to show no change in the conductivity if the acetic acid solution when aluminium hydroxide is added to it. But if an acetate is formed, the conductivity ought to inccrease considerably, for acetic acid, being a weak acid, has small conductivity, but its salts are good conductors. As a matter of fact, we have found that the conductivity of an acetic acid solution does not change appreciably when freshly precipitated aluminium hydroxide or ferric hydroxide or chromium hydroxide is dissolved in it, whilst the solution of zinc hydroxide in acetic acid causes a great increase in conductivity. Hence we can infer that the hydroxides of aluminium, chromium, and iron become peptised in acetic acid, whilst zinc hydroxide maily forms zinc acetate with acetic acid. These results are corroborated by the fact that zinc hydroxide is a much stronger base than ferric, aluminium or chromium hydroxide.

We have already mentioned the peculiar behaviour of the products obtained by mixing together a metallic salt (capable of forming an insoluble hydroxide), ammonium or alkali hydroxide, and glycerin or a concentrated solution of sugar. We get or do not get a precipitate of the hydroxide according as we add the salt solution to a mixture of glycerin and hydroxide or the hydroxide to the mixture of the salt and glycerin. The clear solutions obtained in the latter case may be either due to the formation of a soluble compound of the hydroxide with glycerin or a colloidal solution of the metallic hydroxide. If a chemical compound is formed, new ions must appear, and the conductivity of the solution must differ from that of the one in which the metal gets precipitated as hydroxide, even though equal quantities of the reagents are taken in both the cases. But if the clear solutions are formed on account of the petisation of the hydroxide in glycerin, there is, from the ionic point of view, no difference in the nature of the two solutions, and hence there should be no difference in conductivity of the two solutions.

(6) Gold chloride, glycerin, and ammonia. (a) Clear solution

(b) Precipitated solution

...

0'0014 0'0014

We find from the above that the conductivities of the two solutions are the same, and hence the ionic conditions of the two liquids are identical. We can, therefore, say with confidence that the clear solution is not due to the formation of any soluble complex, but only a peptised solution of the hydroxide. That they are really peptised solutions is further shown by the fact that a slight rise in temperature brings about a precipitation of the hydroxide, the same change also taking place if the solutions are kept for some hours.

When an alkali hydroxide is added to a solution of a copper salt, a blue hydroxide of copper is precipitated, which on warming becomes black, due, probably, to the formation of a compound less hydrated. But if during precipitation a trace of the copper salt remains undecomposed, the blue hydrate cannot be changed into the black one by any amount of boiling. The undecomposed salt cannot be completely removed by washing with cold water, and it seems probable that the undecomposed salt becomes absorbed by the blue hydroxide and stabilises it. Washing with hot water removes the undecomposed salt, and then the precipitate becomes black. We have observed that if to this black hydroxide a little of the copper sale be added and the whole boiled, a reversible change takes place and the blue precipitate reappears.

The next point for investigation was whether different alkali hydroxides have different actions on the stabilisation of the blue hydrate or not. In this connection certain striking observations were made. In order to make a rough quantitative idea, icc. of copper sulphate or copper

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a

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chloride solution was taken in every case, measured amount of the alkali of known strength was run in from a burette, and the total volume was made up to 40 cc. in a boiling tube. boiling tube was next put in a large beaker containing boiling water, and the time taken by each to turn black was noted. It must be emphasised that this being a case of reaction in heterogeneous medium, the results in some cases could not be exactly reproduced, but on the whole the following conclusions have been drawn from a large number of experiments :

(1) The stronger the alkali, the quicker is the transformation from the blue to the black modification; thus taking equal concentrations of KOH, NaOH, Ba(OH)2, Sr(OH)2, Ca(OH)2, and aniline, it was observed that KOH blackened first. It was also observed that KOH transformed much more quickly than NaOH.

(2) The behaviour of calcium and strontium hydroxides is very peculiar. Here with an excess of alkali there are more than one stage at which a complete retardation of the change

It is well known that in presence of an alkali, the blue freshly precipitated hydroxide of cobalt becomes pink. Now this change is exactly of the same type as the conversion of the blue copper hydroxide to the black variety. In this case also a trace of the undecomposed cobalt salt, nitrate, for example, gets absorbed by the blue hydroxide and stabilises it, and we cannot get the pink variety of cobalt hydroxide if there is a little undecomposed cobalt salt left. Just as in the case of copper, warming of the black variety with a little copper salt regenerates the blue variety, in the case of cobalt warming of the pink form with

a

little cobalt salt also regenerates the blue variety, but in the latter case the cobaltons hydroxide begins to be oxidised in presence of air.

All those salts which produce a hydroxide soluble in excess of caustic alkali, namely, salts of zinc, aluminium, tin, lead, &c., markedly retard the transformation of both the blue copper hydroxide to the black form as well as that of the blue variety of the cobalt hydroxide to the pink form. It seems probable that the presence of aluminium hydroxide, lead hydroxide, tin hydroxide, &c., in the colloidal state tends to peptise the cobalt hydroxide or the copper hydroxide.

Benedict (Jour. Amer. Chem. Soc., 1904, xxvi., 695) casually observed that if an excess of a caustic alkali be added to the solution of a cobalt salt, the blue hydroxide which is at first formed does not change into the pink variety if a nickel salt be present. The greater is the retardation, the greater is the amount of the nickel salt originally present in the solution. Benedict did not give any explanation of this peculiarity, neither did he mention the action of other salts on the rate of transformation of the blue to the pink modification. The effect of the presence of salts like ferrous ammonium sulphate, zinc sulphate, manganese sulphate, ferric chloride, chromium sulphate, potash alum, nickel chloride, tin chloride, lead nitrate, cadmium chloride, copper sulphate, magnesium sulphate, calcium chloride, thorium nitrate, strontium nitrate, and uranium acetate has been investigated, and it has been observed that only the nickel salt produces a remarkable retardation. The next to produce the greatest retardation seems to be a calcium salt, but there is a great fall in retardation from nickel to calcium. The transformation of blue copper hydroxide to the black variety is also retarded by nickel salts. It is interesting to note that though a soluble nickel salt added to a cobalt salt before the addition of the alkali retards the change of the blue to the pink form, the reaction is not reversed upon the subsequent addition of the nickel salt to cobalt hydroxide. Neither is there any effect when nickel hydroxide is added instead of a soluble nickel salt, though undoubtedly the hydroxide of nickel is formed when excess of