June 24, 1921] 



SCIENCE 



579 



A quantitative study of adsorption in solution 

 and at interfaces of sugars, dextrin, sta/rch, gum 

 arable and egg albumen, and the mechanism of 

 their action as emulsifying agents: George L. 

 Clark and Wm. A. Mann. By the most accurate 

 method known — ^the use of the stalagmometer for 

 measurement of interfacial tension and the Morgan 

 drop weight apparatus for measurement of surface 

 tension of single liquids — the adsorption of sugar 

 in solution has been determined to be negative, 

 the adsorption increasing in ratio with increase 

 in concentration of sugar, while the adsorption of 

 sugar at the interface is positive and increases 

 in the same ratio as in solution. Dextrin and 

 starch, in very dilute solutions, are negatively ad- 

 sorbed in solution but, in more concentrated solu- 

 tions,, are positively adsorbed while at the inter- 

 face they are negatively adsorbed — starch more so 

 than dextrin. Gum arabic behaves, in this re- 

 spect, in the same manner as starch. A favorable 

 surface tension, seemingly, is not a prerequisite 

 for a good emulsion with any solution studied, al- 

 though viscosity is an important factor. Better 

 emulsions have been obtained with egg albumen — 

 saturated solutions — ^than with any other solution 

 under inspection. 



The preparation, properties and molecular vol- 

 ume relationships of the ammines and hydrates of 

 eobaltous fluoride, bromide, nitrate, carbonate and 

 citrate: George L. Clark and H. K. Buckner. 



The molecular volume compression of the sub- 

 sidiary valence groups, NH3 and HoO, were studied 

 in the same manner as in the previous work on the 

 chloride and sulphate of cobalt (J. Am. Chem. Soc, 

 42, 2483 (1920)) in light of difference in volumes 

 between anion and cation and possibilities of space 

 cavities. It was confirmed that the larger the 

 difference between anion and cation the greater the 

 possibility of cavities, and the less the compression 

 of NH3 and H2O required the more stable the 

 compound and the greater the possibility of hold- 

 ing a maximum number of groups. The various 

 compounds prepared and studied are distinctly 

 new with the exception of eobaltous bromide hex- 

 ammine and eobaltous nitrate hexammine, the 

 following being representative: eobaltous fluoride 

 hexammine, eobaltous nitrate di-hydrate, am- 

 mines of eobaltous nitrate indicating more than 

 six subsidiary valence groups and ammines of eo- 

 baltous carbonate and citrate. 



Emulsification with soaps of linoleic and rici- 

 noleic acids: George L. Clark and H. K. Bdck- 



ner. This work has involved the quantitative 

 study by means of surface energy measurements 

 for solutions and at the interface between aqueous 

 solution and a pure oil by the drop weight method 

 of the following points : the solubility in water of 

 the free acids from the log. concentration-surface 

 tension curve; the adsorption at the surface and 

 the volume occupied by each molecule in the sur- 

 face; the surface tensions of various concentra- 

 tions of the soaps in solution, the effect upon the 

 interfacial tension between water and pure toluene, 

 the effect of the hydrolysis of the soap and the 

 prevention of hydrolysis by the addition of va- 

 rious concentrations of NaOH to a given concen- 

 tration of the soap; a test of the antagonistic 

 effect of sodium and calcium soaps by testing the 

 effect upon the interfacial tension between water 

 and toluene containing a small amount of the free 

 acid of adding various salts of sodium and cal- 

 cium, resulting in the fact that the sodium salt 

 promotes emulsions of oil in water and calcium 

 salts promote emulsions of water in oil; and finally 

 a thorough comparison of all the data so ob- 

 tained with previous work on soaps of palmitic, 

 stearic and oleic acids. All results of this purely 

 quantitative study are necessarily nimierical and 

 can not be included in a short abstract. 



Notes on the preparation of pure platinum: Ed- 

 ward WiCHERS. The paper briefly states the 

 method used in preparing platinum sponge free 

 from other platinum metals and base metals, and 

 describes in more detail the work that has thus 

 far been done on the conversion of this sponge to 

 compact metal with minimum contamination. 

 E.M.F. tests show the resulting platinum to be 

 of higher purity than the best previously obtain- 

 able, i.e., the thermoelement wire of Heraeus, and 

 show the difference in purity to be a matter of 

 calcium content. Results of experiments with 

 magnesia refractories are also given. There is a 

 brief outline of further work to be done on this 

 subject. 



Modified method for tlie determination of iron 

 and vanadium after reduction by hydrogen sul- 

 phide: G. E. P. LUNDELL and H. B. Knovstles. 

 Published methods for the determination of iron 

 and vanadium after reduction by hydrogen sul- 

 phide ordinarily yield high values. A modified 

 method which is sufficiently accurate for most 

 purposes is presented, and a procedure for ac- 

 curate analysis is outlined. 



The free energy of dilution of hydrobromic add; 

 the activities of its iOTis in very dilute and con- 



