656 RUBBER 



produce an inferior rubber on this same account. The 

 effect, however, may not be very marked, as small 

 dilutions of latex do not show very marked effects. 

 Secondly, in the preparation of sheet rubber it is essential 

 to add a certain amount of water to the latex, in order 

 to avoid certain defects, which, although of no real 

 significance, affect the market price of the commodity. 

 If it is shown that dilution, even to the extent necessary 

 in the preparation of sheet of good even appearance, 

 affects the quality, such dilution will have to be avoided, 

 at the expense of appearance, which is a poor criterion 

 of value. 



Only a few remarks need be made on the subject of 

 latex collection, which are really summed up in the word 

 " cleanliness." 



Cleanliness in collection and rapidity of collection 

 means more rubber from " first quality " latex, since any 

 extraneous matter or residues in cups may set up fer- 

 mentation very rapidly and cause partial or complete 

 natural coagulation and a lower percentage of No. i 

 rubber. 



I would point out here, however, that this naturally 

 coagulated rubber, although it fetches a comparatively 

 low price on account of irregular and general dark colour 

 due to surface oxidation, is probably of very high quality 

 owing to the conditions under which it is coagulated, i.e., 

 a rich concentrated latex containing higher proportions 

 of caoutchouc, protein, salts, etc. The proportion of 

 first quality latex rubber to naturally coagulated lump 

 should amount to between 70 and 80 per cent. 



Coagulation. 



The method of coagulation is a very important factor 

 from the point of view of the ultimate product, and much 

 remains to be investigated in connection with the under- 

 lying causes fo>r the differences obtained under different 

 conditions of dilution and with different coagulants. 



I propose to discuss this subject entirely from the 

 practical point of view, and thus to deal with only the 

 principal coagulants which have been or are at present 

 in use. 



