298 



SCIENCE 



[N. S. Vol. LII. No. 1343 



Diffusing power of pigments: W; K. Lewis and 

 P. P. Bakek. The diffusing power of pigments 

 can be determined hy measuring the weight of 

 pigment per unit of cross sectional area necessary 

 to obscure objects behind a suspension of the 

 pigment, the result being expressed as square 

 centimeters per gram or square feet per pound. 

 The determination can be carried out in simple 

 apparatus and results can be checked with ac- 

 curacy. It is believed that the diffusing power is 

 .the most satisfactory measure of the fineness of a 

 pigment; and as such is of obvious interest and 

 value to the rubber trade. 



The effect of compounding ingredients on the 

 physical properties of rubber: C. Olin North. 

 Compounding experiments in which from one to 

 fifty volumes of filler, i. e., gas, black, zinc oxide, 

 etc., were added to 100 volumes of rubber are de- 

 scribed. The values obtained for tensile strength, 

 etc., are corrected back to the actual volume of 

 rubber present and another set of curves drawn. 

 Tensile strength calculated on area at rest is un- 

 fair to a soft stretching stock. Tensile at break is 

 suggested as a better basis of comparison. This 

 is obtained by multiplying usual tensile strength 

 by final length and dividing by the original length 

 times a correction factor, because of volume in- 

 crease during a stretching. A visual picture of 

 the physical structure of rubber, i. e., network 

 hypothesis based on the assumption that large col- 

 loidal aggregates function as elastic fibres and 

 the smaller as plastic material is presented. Vul- 

 canizaition probably locks up these fibers to form a 

 network. 



The microscopic examination of rubber and 

 rubber, products : Henry J. Masson and Irene C. 

 Diner. The authors presented the results of their 

 investigation in the line mentioned in the title. 

 Magnifications of from 500 to 2,000 diameters 

 were used. Best results were obtained at mag- 

 nifications of about 800 diameters. The ordinary 

 methods of metallurgy were resorted to, both ob- 

 lique illumination and vertical illumination being 

 used. Photomicrographs were shown at the meet- 

 ing of various samples which had been examined. 



Subber chemistry from the colloidal viewpoint: 

 Ellwood B. Spear. The mechanism of crystalli- 

 zation, condensation, polymerization and coagula- 

 tion was discussed. Gelation is one type of coagu- 

 lation. Selective adsorption is given as a reason 

 for the increased tensile strength of compound 

 rubber. This deals with the different surface 



energy of rubber and the various compounding 

 ingredients. 



leather chemistry section 

 Louis E. Levi, chairman 

 William Klaber, secretary 



The true tanning value of vegetable tanning ma- 

 terials: John Arthur Wilson and Erwin J. 

 Kern. A new method of tannin analysis is de- 

 scribed which determines exactly what is called 

 for in the generally accepted practical definition 

 of tannin, namely, that portion of the water-sol- 

 uble matter of certain vegetable materials which 

 will precipitate gelatin from solution and which 

 will form compounds with hide fiber which are 

 resistant to washing. The analyses of 10 common 

 tanning materials by the new method and by the 

 official method of the American Leather Chemists ' 

 Association indicate that the latter method is in 

 error to the extent of from 43 to 220 per cent. 

 The new method gives reproducible results and is 

 considered entirely practicable. 



The neutral salt effect and its bearing upon 

 leather manufacture: John Arthur Wilson and 

 Edwin A. Gallun. The addition of neutral salts 

 to the various liquors used in making leather is 

 shown to have the effect of increasing the activity 

 of all the constituents of such liquors, whether 

 they be acid or alkaline. In the case of chloride 

 salts, this was shown quantitatively to be due to 

 removal of solvent by hydration of the added salt. 

 The results of 37 experiments in chrome tanning 

 with different kinds and proportions of neutral 

 salts are given which throw considerable light 

 upon the meohanism of chrome tanning. 



The determination of sulfate in sulfonated oils: 

 Erwin J. Kern. In the determination of un- 

 oombined sulfate in sulfonated oils, the use of 

 organic solvents can be dispensed with, if the usual 

 brine solution be reijlaced by a 10 per cent, solu- 

 tion of monosodium phosphate, which gives a clear 

 separation of solution and oil in very few minutes. 

 After boiling the oil with hydrochloric acid, total 

 sulfate may be determined in the same way. The 

 phosphate solution extracts all of the sulfate in 

 each case, which may then be determined as barium 

 sulfate in the usual manner. A saving of time 

 is effected by the new method. 



A new method for the determination of sulfuric 

 acid in leather: Arthur W. Thomas. 



Time factor in the adsorption of the constituents 

 of chromi sulfate solutions by hide substance: 

 Arthur W. Thomas and M. J. Kelly. 



