170 Biffen . — The Coagulation of Latex . 
rubber itself, and that the cause of coagulation must be looked 
for in the medium in which they are suspended. 
From our knowledge of the constitution of latex it is 
evident that the proteids are the most likely substances to 
cause this when treated with acids, alkalies, excess of salt, & c., 
and when boiled. 
Unfortunately few latices have as yet been examined for 
their proteid constituents, chiefly on account of the difficulty 
of obtaining them in their natural condition in European 
laboratories, owing to their coagulating and undergoing 
decomposition during the journey from the tropics 1 . The 
investigations so far made prove the presence of albumin, 
globulin, albumose, and peptone in several rubber-yielding 
latices 2 . In the clear solution left after separation of the 
rubber-particles the xanthoproteic reaction always showed the 
presence of proteid matters, but under the circumstances 
it was impossible to identify them. 
Now albumins are characterized by the coagulation of their 
solutions on heating, especially in the presence of dilute acids, 
and globulins by their ready precipitation with the salt- 
solution and their coagulation on heating. 
Thus when the latex of Hevea brasiliensis is held in the 
smoke of the burning urucuri nuts, the albumin it contains 3 
is clotted by the action of heat in the presence of dilute acetic 
acid. 
The globulin of Manihot Glaziovii latex coagulates on 
heating when the temperature rises to 74-76° C. 4 
The acid latex of Castilloa elastica contains an acid albumin, 
which on neutralization forms a gelatinous precipitate. 
These coagula on forming gather up the rubber-particles 
(and probably starch-grains also, in the case of starch- 
containing latices) in the same way as the white-of-egg gathers 
1 This does not apply to the latex of Mimusops Globosa, or Hancornia speciosa , 
both of which may be kept for months without undergoing any change. 
2 J. R. Green, Proc. Roy. Soc. 1886, p. 28. 
3 Faraday — see Le Caoutchouc et la Gutta-percha. 
4 J. R. Green, ibid. 
