5«6 



NATURE 



[December 29, 192 1 



pilchards. The kinds of organisms eaten depend on 

 the phase of the fish- — they are larval gastropods, 

 diatoms and flagellates, larval molluscs and Crustacea 

 in the case of the herring ; green (chlorophyllian) 

 organisms, copepod eggs and larvae, and copepods 

 (sprat) ; copepod eggs, larvae and adults, then mud- 

 containing unicellular organisms, and finailv mol- 

 luscan larvae in the case of the pilchard. A remark- 

 able result is the great proportion of larval fishes 

 which contain no apparent food, and this observa- 



tion may lead to most valuable results if it can be 

 shown that there is a correlation between the number 

 of empty stomachs find the poverty of the sea in the 

 necessary food-organisms. In that case we should have 

 an easily observed measure of the coincidence between 

 the period of abundance of larval fishes with that of 

 sufficient food, or vice versa, and this is obviously the 

 kind of datum required in order that we mav be able 

 to forecast good or bad fishery years. Obviously, the 

 work noticed is of much importance. J. J. 



The Need for Research in Colloid Chemistry.^ 

 By William Claytox. 



COLLOID chemistry has never been discussed so 

 frequently as it is to-day. Its comparatively 

 recent growth and development, and the fact that its 

 ramifications extend into every field of chemical re- 

 search and industry, seem to be leading chemists to 

 turn to colloid chemistry as a possible panacea for 

 their numerous and varied difficulties. Certain it is 

 that no branch of applied chemistry to-dav can be 

 declared free from colloid problems, and that the 

 chemistrx' of to-morrow will be coLoid chemistry, pure 

 and applied. 



Prof. Bancroft's compilation of two hundred re- 

 search problems adequately serves, not only to demon- 

 strate the wide industrial applications of colloid 

 theory, but also to show the present position of the 

 theoretical science itself with its too frequently purely 

 empirical generalisations. He devotes seventy-one of 

 his problems to a consideration of adsorption pheno- 

 mena — a correct proportion, no doubt, since adsorp- 

 tion data can be obtained in a very definite quantita- 

 iive way, and the results admit of immediate and 

 varied application. 



.\dsorption is now recognised as playing a deter- 

 mining influence in heterogeneous catalysis, emulsions, 

 fogs and smokes, surface tension, stability of solu- 

 tions, coagulation and precipitation, etc. Prof. Ban- 

 croft pays particular attention to adsorbed gas films 

 and their influence in contact catalysis. Notable 

 progress in this field has been made by Langmuir in 

 America, who has adduced good evidence that such 

 adsorbed films are of monomolecular thickness. That 

 stable films can exist at atmospheric pressure can be 

 argued from several efTects, e.g. catalytic poisons, 

 passivity, over-voltage, and lubrication. 



Under adsorption Prof. Bancroft details problems 

 in flotation and wetting power, pointing out that no 

 systematic study of the selective adsorption of liquids 

 by solids has yet been published. Quantitative work 

 is urgently needed in this connection, especially as the 

 literature on the flotation of ores contains many 

 papers lacking' in sound colloid chemistry. 



The caking of powders, setting of cements, 

 behaviour of coarse and fine powders in liquids, and 

 the reversibility of the calomel electrode are a few of 

 the many problems involving adsorption phenomena. 



One problem (No. 56) is of outstanding importance, 

 viz. "the quantitative adsorption of dyes by alumina, 

 stannic acid, etc., with sjjecial reference to hydrogen- 

 ion concentration." The work of Jacques Loeb on the 

 effect of various electrolytes on gelatin in solutions, 

 with definite hydrion concentrations, has placed the 

 chemistry of gelatin, casein, and other amphoteric 

 proteins on an entirely new footing. Such proteins 

 possess a certain ^H value Indicating neutrality (gela- 



^ " Rescrch Problems in Colloid Chemistry." By Wilder D. Bancroft' 

 Member of the Committee on the Chemistry of Colloids : National Re«earch 

 Council. Reprint and Circular Series of the National Research Council 

 (U.S.A.). No. 13(1921). so cents. 



tin, /)H=4-7). When the pH value exceeds the 

 neutrality figure the protein behaves as an acid, com- 

 bining with cations ; when the pW value is less, the 

 basic tendencies are pronounced and combination with 

 anions occurs. In the light of this work such familiar 

 generalisations as the Hofmeister series of ions or the 

 Pauli series of acids present no real existence, since 

 the /)H values were not measured. Membrane per- 

 meability, dye-staining, and certain physiological 

 phenomena must all be referred to measured hydrion 

 concentrations. 



On the subject of emulsions Prof. Bancroft rightly 

 points out that, whilst the problem of making emul- 

 sions has been well investigated, the converse, break- 

 ing of emulsions, has not been so thoroughly studied. 

 Stable emulsions are only too frequently a source of 

 great trouble in industrial operations, and work on the 

 theoretical principles involved in devising means for 

 their coagulation or separation is very desirable. In 

 this connection, too, it is pointed out that, in the cen- 

 trifuging of colloidal systems, no systematic study has 

 been made connecting the quantitative relations 

 between density, size of particles, and number of 

 revolutions per minute necessary to cause pre- 

 cipitation. 



Mention is made of the recent work of Holmes and 

 Child, who failed to find evidence for the adsorption 

 of gelatin at the oil-water interface in kerosene/water 

 emulsions. This result contradicts the observation of 

 Winkelblech, who proved that gelatin concentrates at 

 the dineric interface when organic liquids are shaken 

 with water. In any case, the effect of adsorbed films 

 or protective layers of the emulsifying agent in emul- 

 sions still leaves much room for inquiry. The old 

 problem of effect of oil concentration on the type of 

 emulsion is brought up once more. Prof. Bancroft 

 doubting the accuracy of Bhatnagars recent woriv on 

 the reversal of phases in oil and water emulsions. 



A problem of direct industrial importance is referred 

 to in connection with the saponification of fats with 

 lime. It is tentatively put forward that water is the 

 real hydrolysing agent, and that the lime is im- 

 portant because the calcium soap which is formed 

 causes the water to emulsify in the fat, instead of the 

 fat in the water. In this connection-iT is of interest 

 to refer to Weston's recent work on the use of col- 

 loidal clay as an emulsifier-catalyst in the saponifica- 

 tion of oils and fats. 



Finally, we can only briefly mention one other 

 important field discussed by Prof. Bancroft, viz. the 

 formation and stability of colloids in non-aqueous 

 liquids. The nature of the stabiliser present in such 

 solutions, the peculiar behaviour of the alcohols with 

 silver alcosol, the formation of jellies in organic 

 liquids, the chemistry of the cellulose esters, the be- 

 haviour of mixed colloids in non-aqueous solvents — 

 these are but a few of the problems requiring inves- 



NO. 2722, VOL. 108] 



