6o 4 SCIENCE PROGRESS 



the feasibility of making "wet" block by means of acid-coagula- 

 tion in the presence of creosote, as an antiseptic. They argued 

 that a certain percentage of moisture in raw rubber had a 

 beneficial effect on its keeping qualities. Brazilian Para always 

 holds about ten per cent, of water. Their wet block was 

 prepared directly from the clots by pressure ; no trouble need 

 be taken afterwards to thoroughly dry it, since it is permanently 

 cured by the creosote. So far this idea has not been put into 

 practice by the planters, neither have buyers evinced a desire 

 for this kind of rubber. The chief difficulty would be to keep 

 the percentage of moisture constant. Manufacturers naturally 

 want to know how much pure caoutchouc they are buying in 

 the raw article. At present they know that dry plantation 

 rubber contains practically no extra weight in the way of 

 moisture. As some one remarked, " Why pay freight on 

 moisture? We can get enough of it in Britain for all our needs!" 

 A word as to cleanliness. Planters now see the great 

 importance of paying strict attention to this in the preparation 

 of raw rubber. Metal collecting vessels, on account of their 

 liability to rust and so to stain the latex, have been discarded 

 in favour of glass. In fact, as in butter and cheese making, 

 metal utensils and appliances should be avoided as much as 

 possible in the manipulation of the latex. There is much 

 similarity between a rubber factory and a modern dairy. 



Yield 



The rubber-producing capacity of cultivated Heveas has in 

 the past been generally under-estimated, and even now the full 

 extent to which it may ultimately reach, as the trees mature, 

 cannot be said to have been gauged with any degree of accuracy. 



An average of one and a half pounds per annum for a tree 

 twelve years old was the original calculation for Ceylon, but 

 this was before wound-response had been taken into account. 

 In Malaya six-year-old plantations are now giving 10 oz. to 

 i lb. per tree, an amount gradually advancing to 3 lb. as 

 the trees reach an age of ten years ; higher subsequent yields 

 are expected. A few old, well-developed trees have given 12 

 to 25 lb. each per annum. Eight seventeen-year-old Heveas in 

 the Perak State, of an average girth of 55 inches, have supplied 

 28| lb. of dry rubber per tree. 1 



1 India-Rubber Journal, 1909, 38. 239. 



