r46 The Ohio Naturalist [Vol. X, No. 6, 



THE FILM TEST FOR CRUDE RUBBER.* 



Chas. p. Fox. 



Buvers of Crude Rubber are sometimes perplexed in their 

 efforts to determine the origin of new or uncommon varieties of 

 rubber bv their usual physical characters. Consequent!}' an 

 easv 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 Torrey (India Rubber Journal, Nov. 1907) as follows: 

 "Some years ago Torrey 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 

 ivhite 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 bv 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 dift'erence 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 finallv 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. meetinsi of the Ohio Acad, of Sci. 



