520 



SCIENCE 



[Vol. LVI, No. 1453 



ties of their components. From these and com- 

 pounding results, the writers are of the opinion 

 that a definite relation can be worked out between 

 solvating action and the effects of softeners on 

 the stress-strain curve. 



The measurement of temperature in ruljljer 

 articles iy means of thermocouples: Ellwood B. 

 Speae and J. F. Ptjedy. Measurements of the 

 temperature in rubber articles by thermocouples 

 are all too low where the depth of insertion is 

 not great, 1-3 inches, and where there is at the 

 same time a temperature differential along the 

 buried portion of the thermocouple wires. The 

 correction to be applied depends upon the depth 

 of insertion, the size of the wires constituting the 

 thermocouple, and the temperature differential. 

 A nsAV method is given for measuring the tem- 

 perature in pneumatic and solid tires. Correction 

 curves are given for use where ordinarj- thermo- 

 couples have been employed. 



The limitations of the obscuring power test for 

 compounding materials: Ell wood B. Speae and 

 H. A. Endees. Experimental evidence is pre- 

 sented in this article that the obscuring power 

 test for compounding materials is unreliable and 

 often misleading in the region where the diameter 

 of the particles is in the neighborhood of one 

 fourth the wave length of light, viz., 0.1 mu. 



The crystallization of sulfur in rubier and the 

 phenomenon of "blooming." I: Heebeet A. 

 Endkes. a solution of sulfur in rubber exhibits 

 the same phenomena of diffusion, crystallization 

 and super-saturation as are shown by solutions of 

 sulfur in other solvents. When rubber saturated 

 with sulfur at e&lendering or vulcanizing tem- 

 peratures is cooled, the solubility is exceeded and 

 the excess sulfur separates as super-cooled 

 globules, dendrites or stable rhombic crystals, de- 

 pending upon the rate of cooling. Sulfur bloom 

 is always composed of rhombic sulfur; the stable 

 form at room temperature. It may be caused by 

 crystallization at the surface of the rubber, either 

 directly from solution or by transformation from 

 super-cooled globules or dendrites. 



The microscopic examination of rubber com- 

 pounds containing antimony pigments: A. F. 

 Harbman. To secure a section of a rubber com- 

 pound sufficiently thin for microscopic examina- 

 tion, some method of hardening must be employed 

 previous to sectioning. Sulfur monochloride has 

 been successfully used for this purpose, but the 

 reagent attacks and destroys the identity of the 

 sulfides of antimony. A bath of molten sulfur 

 may be used to produce the required rigidity 

 without materially altering the appearance of 



the antimony pigments. Photomicrographs illus- 

 trating the new method are shown. 



The resilient energy and abrasion resistance of 

 vulcanized rubber: H. W. Geeidee. A study has 

 ■been made of the eft'eets of several compounding 

 pigments upon the abrasion resistance of vul- 

 canized rubber. It was found that gas black 

 gives the greatest resistance to abrasion, followed 

 by light magnesium carbonate, china clay, zino 

 oxide, colloidal barium sulfate and lithopone, in 

 the order named. There is found to be a rela- 

 tionship, but not a direct proportionality, between 

 tensile strength and abrasion resistance for 

 rubber compounded with reinforcing pigments. 

 Kesilieut energy gives an approximate index of 

 abrasion resistance with gas black, magnesium 

 carbonate, china clay and zinc oxide, but it is not 

 a measure of abrasion resistance with colloidal 

 barium sulfate or lithopone. The data appear to 

 show that hardness (or rigidity) is also a factor 

 in resistance to abrasive wear. The product of 

 resilient energy and hardness is suggested as an 

 index of toughness. Some principles are sug- 

 gested which may be of value in compounding 

 rubber to obtain high resistance to abrasion, 

 including the use of high-grade accelerated mix- 

 ings and combinations of reinforcing pigments 

 in such proportions by volume as to give proper 

 rigidity combined with high resilient energy. 

 Combinations of gas black and magnesium car- 

 bonate in suitable proportions are found to give 

 high resistance to abrasion, high resilient energy 

 and considerable hardness and rigidity. 



Persistence of calender grain after vulcaniza- 

 tion. (Lantern) : W. B. WiEGAND and H. A. 

 Beaendle. 



A study of the relation of the structure of 

 mercaptobenzothiazole and its derivatives to their 

 value as accelerators of vulcanization. (Lantern) : 

 L. B. Sebeell and C. E. Booed. The preparation 

 of mercaptobenzothiazole dorivatives by the 

 methods reported in a previous paper has been 

 extended to include several new mercaptothiazoles 

 not previously described. Other compounds hav- 

 ing a similar structure have been prepared and 

 their curing power compared with that of mer- 

 eaptobenzotldazole. In this way the particular 

 grouping responsible for the activity of mercapto- 

 benzothiazole as an accelerator has been identi- 

 fied. The effect of subatitutents in the benzene 

 nucleus of mercaptobenzothiazole upon its activity 

 as an accelerator has also been studied. 



Charles L. Paesons, 



Secretary 



