April, 1910.] 
The Film Test for Crude Rubber. 
i47 
in transferring from container to slide. The term “figure” is 
rather indefinite. In the experiment quoted it is not made clear 
whether shape or color or character of film is to determine. 
We assumed that a combination of both character of film and 
its color was to be used. Shape of film is mere matter of 
accident. Draft of air, declivity of table, skill of the operator, 
all help to modify shape. 
“The viscosity of the solution will determine the thickness of 
the film and will control the size, shape and number of vesicles. 
The most important factors to be reckoned with are colour and 
dirt (suspended matter).” 
We made the test very thorough, and examined in all, about 
twenty-five kinds of crude rubber. Each test was made in 
duplicate. The dry film was held for a moment in the fumes of 
sulphur chlorid. This treatment did not alter the film but 
removed the tackiness. Slides prepared in this way keep 
indefinitely, do not stick together and are free from dust. In 
this way definite comparisons between a large number of films 
could be easily and quickly made. 
We found that it was not a difficult matter to obtain similar 
duplicates from the same solution when made at same time. 
Exactness was an impossibility. In some cases the difference 
between duplicates were great enough to assign different names 
to the same samples. We used much care in getting authentic 
samples and in each case have compared the crude physical 
characters with the descriptions given by reliable authorities: 
Pearson, Brandt, Falconette, and Clouth. 
Throughout the entire work we could not definitely determine 
a film peculiar to any one brand of crude rubber. Considerable 
stress was put upon the “Lapori film.” We found this figure 
to be common to many kinds of rubber. Rubbers of different 
botanical and geographical origin often gave this same tvpe of 
film. 
Throughout the experiment there was an indication that the 
character of the film was determined by the viscosity of the 
solution. To test out this idea we made up a series of solutions 
of these rubbers, varying from thin to very thick. 
The table proves the point in question. It clearly shows the 
influence of viscosity: 
