1826.] On pure Caoutchouc. 175 



of putrescent milk; its specific gravity was 1011*74. When 

 exposed to the air in thin films, it soon dried, losing weight, and 

 leaving caoutchouc of the usual appearance and colour, and 

 very tough and elastic : 202*4 grains of the liquid dried in 

 a Wedgewood basin, at 100 Fahr., became in a few days 

 94'4 grains, and the solid piece formed being then removed 

 from the capsule, and exposed on all sides to the air until 

 quite dry, became 91 grains : hence 100 parts of sap left nearly 

 45 of solid matter. 



Heat caused immediate coagulation of the sap, the caout- 

 chouc separating in the solid form, and leaving an aqueous 

 solution of the other substances existing with it in its first 

 state. 



Alcohol poured into the sap in sufficient quantity caused a 

 coagulum and a precipitate, both of which were caoutchouc of 

 considerable purity. The alcohol retained in solution the ex- 

 traneous matters, which, possessing peculiar properties, will be 

 hereafter described. 



Solution of alkali added to the sap evolved a very fetid 

 odour, but did not appear to exert any particular action on the 

 caoutchouc. 



The sap, left to itself for several days, gradually separated 

 into two parts ; the opake portion contracted upwards, leaving 

 beneath a deep brown, but transparent solution, evidently con- 

 taining substances very different in their nature from caout- 

 chouc itself, and which, considering the specific gravity of the 

 sap and of pure caoutchouc (the latter being lighter than water), 

 were probably present in considerable quantity. 



It was found that, by mixing the sap with water, no other 

 change took place than mere dilution. The mixture was uni- 

 form, and had all the properties of a weak or thin sap. Heat, 

 evaporation, acids, and alkali, produced the same effects, gene- 

 rally, as before. 



When the diluted sap was suffered to remain at rest, a sepa- 

 ration soon took place, similar to that which occurred with the 

 native juice, but to a greater extent; a creamy portion rose to 

 the top, whilst a clear aqueous solution remained beneath. 

 Hence it was found easy to wash the caoutchouc, and remove 

 from it other principles which had been generally involved in 

 it to a greater or smaller extent during its coagulation. For 



