3SrOVEMBEB 10, 1922] 



SCIENCE 



549 



Jiigher concentrations it inhibits fixation, as 

 sodium sulfate does at all concentrations. At 

 Pj^-j- = S, both salts decrease the fixation, but 

 not to the same extent. Explanations I'or the 

 tlifferenees isi behavior are given based on the 

 Donnan effect on the collagen and the action of 

 tlie salts in altering the degree of dispersion and 

 •diffusibility of the tannin particles. 



TJtc difference in Jcind or degree of tannin 

 .fixation as a function of the hydrogen-ion con- 

 centration: Arthur W. Thomas and Margaket 

 W. Kelly. It has- been shown that after remov- 

 ing all water soluble substances from freshly pre- 

 pared leather, treatment with alcohol will extract 

 Tarring amounts of tannin depending upon tlie 

 ■hydrogen-ion concentration at which the leather 

 Was tanned. For example, hemlock and gambler 

 leathers tanned at Pjj+ = 3 will yield about 25 

 per cent, of their fixed tannins to alcohol extrac- 

 tion, a smaller amount when tanned at p„+ = 5, 

 ■and practically none ivhen tanned on the alkaline 

 side of Pfj-T- = 5. If the leathers are drastically 

 ■dried before alcoliol extraction, very little alcohol 

 soluble uuit.ter is found. These preliminary ex- 

 periments are to be continued with the view of 

 tlirow'ing more light upon the differences in kind 

 -or degree of tannage at differing hydrogen-ion 

 •concentrations. 



The iannin-gelatin reaction: Arthur W. 

 Thomas and Alexander Frieden. The mutual 

 .precipitation of tannin and gelatin depends to a 

 very large degree upon the hydrogen-ion concen- 

 tration of the solution. It has been shown that 

 the gelatin-salt test for tannin is sensitive to one 

 part of tannin in 110,000 to 200,000 parts of 

 water, depending upon the source of the tannin, 

 sand provided the hydrogen-ion concentration of 

 the solution is adjusted to its optimum. This 

 -optimum varies with, different extracts, ranging 

 from p,.[+ = 3.5 to 4.5. The details are given 

 in the original paper. It is also shown that it is 

 Unnecessary to prepare the gelatin-salt test 

 "reagent daily. This reagent kept for two months 

 ■at summer temperature when covered with a 

 layer of toluene and its delicacy was not impaired 

 in that time. How much longer it would keep 

 Is unknown. 



Are vegetable tannins amphoteric? Arthur W. 

 'Thomas and Stuart B. Foster. Six common 

 vegetable tanning materials were investigated bv' 

 the electrophoresis method indicating that all are 

 ^amphoteric, i. e., changing from anodic migrating 

 to cathodie in the Pjj+ range of 2.5 to 2.0. Hy- 

 ■drogeu-ion concentration precipitation curves are 

 •also given for the extracts studied. 



The practical color measurement of vegetable 

 tan liquors: E. 0. Philltps and L. R. Brown. It 

 is suggested that color measurements are best 

 made by tanning pieces of skin under standard 

 conditions. 



The acidity of synthetic tans: S. KoHX, J. 

 Breedis and E. Crede. The active principles of 

 most synthetic tans are sulfonic acids in the 

 preparation of which an excess of sulfuric acid 

 is used. It is relatively easy to find out whether 

 or not sufficient alkali has been added to neu- 

 tralize this excess. But sulfuric acid being 

 neither the sole nor the worst of the undesirable 

 ingredients occurring in some syntans, it is im- 

 portant to devise methods by which preparations 

 containing undesirable ingredients can be de- 

 tected. To the methods suggested previously a 

 new one is added which is based upon compara- 

 tive observations of the part played by the acidity 

 of syntans in the precipitation of gelatin. 



Tlie colloid chemistry of basic chromic solu- 

 tions: Fraisik L. Seymour- Jones. A review of 

 the literature upon the nature of chromic solu- 

 tions show-ing their very complex and as yet un- 

 settled condition of solution. Ultrafiltration ex- 

 periments failed to show the presen-oe of any col- 

 loidally dispersed chromium compound in the 

 ordinary single bath chrome liquor. The experi- 

 ments are preliminary in nature and further 

 investigation is contemplated. 



The electrophoresis of chromic solutions: 

 Frank L. Seymour-Jones. The Thompson- 

 Atkin theory of chrome tanning, which postulates 

 a negatively charged chromium complex as the 

 tanning agent, is criticized and shown not to be 

 of general application, if at all, since chromic 

 solutions which did not show any evidence of 

 negatively charged chromium complexes tanned 

 hide powder. It is true, however, that in certaia 

 basic solutions of chromic sulfate, part of the 

 chromium exists in a negatively charged complex, 

 while this does not occur in the basic chloride nor 

 3'et chrome alum. 



The interpretation of the influence of acid on 

 the osmotic pressure of protein solutions : Jacques 

 LOEB. When osmotic equilibrium is established 

 between a solution of casein and hj'droehlorie 

 acid enclosed in a collodion bag and an outside 

 aqueous solution free from protein, the hydrogen- 

 ion concentration is always greater in the outside 

 solution than in the edsein solution. The ob- 

 served osmotic pressure is accounted for quanti- 

 tativelj' by the difference in concentration of 

 hydrochloric acid in the two solutions, without 

 taking into consideration any possible osmotic 



