PARA RUBBER. 131 



loss consists mainly of water, salts, wood fibres, and min3ral 

 impurities. The oily substances form a very small part only of the 

 total extract. Weber states that the resinous matter is generally 

 semi-transparent, yellowish-brown, or brown ; in some cases it is 

 semi-resilient and slightly sticky, sometimes hard and brittle, and 

 ra a few cases is white and powdery in appearance. The estimation 

 of these oily and resinous constituents is best carried out by 

 extracting 5 to 10 grammes of the perfectly dry washed rubber 

 in a Soxhlet extracter by means of acetone. Many persons 

 assume that the percentage of resinous matter in indiarubber is an 

 indication of the care bestowed upon it by the producer. This 

 is not correcl . as the resinous matters exist in the latex as the latter 

 flows from the trees. The variation in the resin of the same brand 

 of rubber is probably due to the condition or age of the tree from 

 which the latex is obtained, or to the mixing of milks of different 

 qualities. 



High Loss undesirable. 



If the loss on washing is beyond a certain amount the rubber 

 will be naturally classed as inferior, and in a paper* read before the 

 [nternational Congress of Applied Chemistry the following interest- 

 jsage occurs: "While fifteen years ago, fine Para rarely 

 showed a loss in washing exceeding from 10 to 12 per cent., this rose 

 within the last ten years from 12 to 16 per cent., and in the last 

 five years had reached from 15 to 20 per cent. During the same 

 tunc Colombia Virgin, at one time one of the finest brands of 

 rubber, has practically entirely disappeared from the market. 

 What little still occurs under the name is an altogether inferior 

 product." _ 



PURIFICATON BY THE GROWERS. 



The use of machinery is bound to become more general 

 when more rubber is collected, and the means adopter! for straining, 

 purifying, and coagulating t he latex will minimise the loss, which nor- 

 mally occurs in the manufacturing process. Already a machine for 

 washing the rubber by the grower has been strongly recommended 

 by Mr. Burgess and others. 



Rubber Washing Machine. 



hi rubber districts a modified wringing machine is frequently 

 u«ed. which, though it is light and cheap, cannot usually be recom- 

 mended as efficient. If a sufficiently powerful and well-equipped 

 rubber washing machine is used, the effect is not only to free the 

 rubber from a large proportion of the soluble impurities, but to 

 produce a dried product possessing good physical properties. 

 A Rubber Washing Machine. 



The following is Mr. P. J. Burgess's account of the new rubber 

 washing machine : — 



"This machine consists essentially of two steel rollers, which 

 revolve on horizontal axes parallel to one another ; the distance 



* India Rubber Journal, Julv 20. 



