148 



The Ohio Naturalist. 



[Vol. X, No. 6, 



TABLE 



After a close examination and comparison of the films given, 

 in duplicate, by samples representing thirtv-three commercial 

 brands of crude rubber belonging to ten distinct groups, we fail 

 to find any indication pointing towards a definite film peculiar 

 to any particular brand of rubber. 



Viscosity seems to be the controlling factor in the formation 

 of a film. Viscosity depends a great deal upon the amount and 

 freshness of the rubber content. With a crude unwashed and 

 dirty rubber, the amount of the rubber will vary, the viscosity 

 will be influenced and the character of the film will be modified 

 according to the purity of the sample. 



Tenacious heavy Para solution gave the honey comb film. 

 Lapori (old) gave a thin transparent film. By adding more 

 rubber to the latter and by diluting the former with solvent, we 

 were able to transpose the character of the films. 



Akron, Ohio, November 2, 1909. 



