RUBBER 655 



from latex containing' 15 per cent., i.e., 1*5 lb., of dry 

 rubber per gallon. This corresponds to a latex density 

 of 0^9898 at 84 F., and I have found recently, by means 

 of a delicate hydrometer, that sheets from a gallon of 

 such latex can be made very even in weight, the difference 

 being about J oz. of rubber per sheet weighing 1*5 lb. 

 in ordinary factory practice. 



If the latex varies from day to day it is impossible to 

 obtain uniformity in the rubber, as varying dilution 

 affects the quality of the coagulum. If such dilution to a 

 standard density, although it enables a uniform rubber 

 to be made, is found to produce a somewhat inferior 

 product, other means may be found to improve the 

 quality of such rubber, since the physical properties of 

 the coagulum probably depend on the relative concen- 

 trations of the caoutchouc, protein, salts, and added 

 coagulant, or of any one or more of these constituents. 

 This point requires investigation, as it may be found 

 that the addition of a salt or of soluble protein material 

 to the latex before coagulation will improve the coagulum 

 and the rubber after vulcanization. 



As far as the primary problem is concerned, i.e., the 

 preparation of the raw rubber, I propose to deal with 

 the problem in a general way in the light of our present 

 knowledge of the subject, and for this purpose shall 

 divide the subject into different sections, treating the 

 various processes in chronological order from tapping and 

 collection of latex to packing, i.e., from the beginning 

 to the end of the history of the sample in its country of 

 origin, in so far as these processes affect the quality of 

 the raw rubber. 



Tapping and Collection of Latex. 



Experiments have shown that excessive tapping causes 

 not only a reduction in the yield of latex, but a reduction 

 in the caoutchouc content and probably of other con- 

 stituents of latex protein, mineral salts, etc. As we 

 know also that dilution of latex produces a weaker 

 coagulum, which has 'been shown to yield an inferior 

 vulcanized rubber, it follows that excessive tapping will 

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