RUBBERS AND GUMS 195 



rubber trees and partly accounts for the ready flow of latex 

 from rubber trees made in tapping wounds in any direction. 



Latex is almost invariably white, resembling milk in appear- 

 ance and consistency, and is essentially an emulsion containing 

 minute globules of rubber, together with resins and proteids 

 associated with the rubber in a watery solution. The globules 

 of rubber vary greatly in size in different species of rubber 

 trees. The specific gravity of latex is ordinarily a little lower 

 than that of water. Latex contains from 48 to 75 per cent, 

 of water, according to the species of the rubber tree, and a 

 variable percentage of resin, proteid, and ash. These latter 

 constituents are considered as impurities and as depreciating 

 the value of the rubber product if they occur in too high 

 percentages. The proportion of proteid, resin, and ash is 

 considerably higher in young than in old mature trees. The 

 percentage of these impurities also varies considerably accord- 

 ing to the species of rubber tree. The lowest percentage of 

 resin, proteid, and ash is found in the latex or rubber of mature 

 Hevea trees. 



The physical constitution of latex being that of an emulsion, 

 the coagulation of the latex may be brought about by any chem- 

 ical or physical process which will disturb the equilibrium 

 in the emulsion and favor the segregation of the solid constitu- 

 ents of the latex. Coagulation of rubber latex has been accom- 

 plished by various methods. The latex of most rubber trees 

 will undergo a spontaneous coagulation within a fairly short 

 time. The latex may also be diluted with water and the 

 whole mixture allowed to stand for 24 hours or more. This 

 method may be used with Ceara rubber as well as with Castil- 

 loa rubber. After standing the rubber, being lighter than 

 water, collects upon the water like cream, while the water 

 remains below. Rubber may also be separated from the watery 

 solution by centrifugal machines similar to the dairy separator. 

 Various other chemical and physical means have been used 

 in coagulating latex. The latex of Hevea and Landolphia may 



