94 



FARA RUBBER. 



Rubber is insoluble in water and also in alcohol, but light 

 coal-tar naphtha, petroleum, spirits of turpentine, carbon disul- 

 phide, ether, benzol, fatty and essential oils cause it to swell, 

 and to a certain extent dissolve it. Gerard states that the best 

 solvent is a mixture of 100 parts of carbon disulphide and 5 1 

 per cent, of absolute alcohol. Strictly speaking, rubber is only 

 partially soluble, as it consists of two substances which have 

 different properties, one of which is easily dissolved ; the other 

 being of a tough elastic consistency which persistently resists 

 nearly all solvents. Seeligmann distinguishes these two isomeric 

 substances as the nervous and adhesive principle respectively. 

 Spence states : * " From my early experiments to determine the 

 amount of the insoluble constituent in raw Para rubber, I came 

 to the conclusion that there was upwards of 8 to 10 per cent, of 

 the product in most samples of raw Para. Later investigation, 

 using chloroform as solvent and extracting over a much longer 

 period, convinced me that my previous observations were wrong. 

 I had not extracted the caoutchouc completely, and, repeating 

 one or two of the analyses, I found that the amount of the 

 insoluble constituent could be reduced to 2 per cent, in samples 

 in which I have previously found about 8 per cent." And in 

 reference to the nitrogen content of the soluble residue : " The 

 highest value obtained was that for a sample of the insoluble 

 product which had. been extracted with chloroform for about 

 three months. It has already been given (5.4 per cent.) and 

 represents at least 33 per cent, of protein in the original 

 product." 



In regard to the complaints about the want of "nerve" in 

 plantation Para as compared with that in the Amazonian 

 product, Beadle and Stevens write : f " The truth of the matter 

 is, that up to now few manufacturers have taken the trouble to 

 give plantation rubber a fair trial. Rubber of such purity has 

 never before been put on the market, and requires mastication 

 and vulcanisation under modified conditions. These conditions 

 we have only discovered after a great deal of experimental 

 work ; and we confidently assert in spite of nebulous talk about 



* Quarterly Journal, Institute of Commercial Research in the Tropics, 

 Liverpool University. 



t India-rubber Journal, p. 321, 7th Oct. 1907. 



