146 
The Ohio Naturalist. 
[Vol. X, No. 6, 
THE FILM TEST FOR CRUDE RUBBER.* 
Chas. P. Fox. 
Buyers of Crude Rubber are sometimes perplexed in their 
efforts to determine the origin of new or uncommon varieties of 
rubber by their usual physical characters. Consequently an 
easy reliable method of determination of variety of crude rubber 
would be of definite value to the trade. Mr. Herbert Wright, 
page 163, 3rd edition of his book, Hevea Braziliensis, in discus- 
sing the structure of crude rubber quotes the experiments of Dr. 
Joseph Torrev (India Rubber Journal, Nov. 1907) as follows: 
“Some years ago Torrev observed that petroleum naptha 
solution of a number of crude rubbers unwashed gave charac- 
teristic figures when a few drops were allowed to evaporate on a 
white surface. The solution consisted of 5 grams of rubber 
dissolved in 100 c.c. of petroleum naptha (6. p 60° to 90° c).” 
“I recall that Fine Para and Matto Grosso were the two 
South American grades, and among the Africans were Lapori ; 
Red Kasai, Upper Congo Ball, Ikalomba and Bussira.’’ 
Fine Para gave always a fine, lace like pattern, Matto Grosso 
gave a similar one, but not so fine and not so regular. Some of 
the Africans gave the same general type of figure but much 
coarser. Others deposited the rubber in a general form of one 
or two nebulous spots shading away very gradually towards the 
edges and connected by a few faint filaments, which were usually 
deposed between two spots in form of a coarse network the mesh 
being approximately circular in form. 
“The most characteristic case of this kind was Lapori. On 
the whole the difference was so great that even an untrained 
observer could without difficulty, identify almost any one of the 
varieties under examination by its figure.” 
The inference to be drawn from the foregoing is that either 
from the method of coagulation or from some other influence a 
certain kind of crude rubber will give a figure peculiar to that 
rubber, and that this figure will serve to identify this rubber. If 
such be the case we have before us an easy, rapid test for deter- 
mining the variety of rubber. 
We gave the “test” a try out. It was soon evident that the 
directions given were somewhat indefinite and the original 
experiments lacked the earmarks of good laboratory technique. 
We finally performed the test by preparing the solution of 
given concentration and using the ordinary microscope slide for 
the film receptacle. We used special care in preparing the 
solution. In many cases it was necessary to use a small spoon 
* Presented at the Nov. meeting of the Ohio Acad, of Sci. 
