ABSTRACTS OF TECHNICAL ARTICLES 609 



conditions of testing are substantially as indicated by the theoretical 

 expression. The theory is then employed to interpret the results 

 of the test and to indicate the best form in which these may be ex- 

 pressed. The general question of testing for flexibility and brittleness 

 is considered in the light of this study. 



Diffusion of Water through Rubber}^ Earle E. Schumacher and 

 Lawrence Ferguson. This article gives data on the diffusion of 

 water through thirteen rubbers of different compositions. The 

 mathematical derivation of a simple formula for calculating the rate 

 of diffusion has been given. The diffusion measurements have shown: 

 (a) that the rate of diffusion of water through a rubber membrane is 

 inversely proportional to the square of the thickness: {b) that the 

 rate of diffusion decreases greatly with increase in hardness; {c) that 

 the effect of saturating the rubber with water is to increase the rate of 

 diffusion through it, due probably not only to an increase in the water 

 vapor pressure within the rubber, but also to a decrease in hardness; 

 {d) that there is no intimate relationship between rate of diffusion and 

 minor variations in the composition of the rubber. 



Effect of Arsenic on Dispersion-Hardenable Lead- Antimony Alloys}^ 

 K. S. Seljesater. Arsenic has no solid solubility in lead and is 

 known to form a continuous series of solid solutions with antimony. 

 Therefore, immediately after annealing and quenching the antimony 

 is in solid solution in the lead, and there is a certain amount of eutectic 

 between the lead-antimony solid solution and arsenic. After quench- 

 ing, the lead-antimony solid solution is supersaturated (the same as if 

 arsenic were not present) and minute crystals of antimony separate. 

 Since arsenic is soluble in antimony, some of the arsenic present will be 

 concentrated in the surface layer of the minute antimony particles, 

 which will then possess surface conditions different from those of pure 

 antimony particles. The condition of the alloy at this stage is 

 analogous to a suspension in a liquid which has been partly stabilized 

 by a third constituent. Agglomeration and precipitation will occur, 

 but at a much slower rate than if the third constituent were not present. 

 Arsenic, therefore, is to be considered as a retardant for the agglomer- 

 ation of minute antimony particles in the lead matrix. The length of 

 the stabilization time decreases at elevated temperatures. The offered 

 explanation is in agreement with the fact that the increase in hardness 

 is practically independent of the percentage of arsenic within limits 

 investigated. The addition of a third constituent insoluble in the 



^^ Industnal and Engineering Chemistry, Vol. 21, February 1, 1929, pp. 158-162. 

 ^* Mining and Metallurgy, Vol. 10, February, 1929, p. 94 (abstract). 



