148 
The Ohio Naturalist. 
[Vol. X, No. 6, 
TABLE 
Concentration 
Kind of Rubber 
Grams 
Para Tribe 
African Tribe 
C'astilloa Tribe. 
Grams in 100 cc. 
“ 1.25 cc. 
Ceylon Black. 
Film given. 
Greasespot film. 
Mongalla. 
Film given. 
Greasespot film. 
C'onche Ball. 
Film given. 
Network film. 
“ 2.50 “ 
Network film. 
Faintly. 
Network film. 
Faintly. 
Wafer film. 
Thin. 
“ 5.00 “ 
Network film. 
Plain. 
Network film. 
Destinct. 
Wafer film. 
Heavy. 
“ 10. 
Wafer film. 
Vesicles. 
Wafer film. 
Wafer film. 
Heavy vesicles. 
“ 20. 
Honey Comb 
Film. 
Wafer film. 
Vesicles. 
Honey Comb 
Film. 
After a close examination and comparison of the films given, 
in duplicate, by samples representing thirty-three commercial 
brands of crude rubber belonging to ten distinct groups, we fail 
to find any indication pointing towards a definite film peculiar 
to anv 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. 
