176 On pure Caoutchouc. [1826. 



this purpose a portion of the sap was mixed with about four 

 volumes of water, and the mixture put into a funnel, stopped 

 below by a cork ; in the course of eighteen or twenty-four hours, 

 when the caoutchouc had risen to the top and occupied about 

 its original volume, the aperture at the bottom of the funnel 

 was opened and the solution drawn off; more water was then 

 added to, and mixed with, the caoutchouc, and the operation 

 repeated, and this was done four or five times, until the water 

 came away nearly pure. During the latter washings, the caout- 

 chouc required a longer time to rise to the surface, in conse- 

 quence of the decreasing specific gravity of the solution in 

 which it was suspended. This was obviated at times, accord- 

 ing to the experiments for which the caoutchouc was required, 

 by performing the first washings with solutions of common salt, 

 muriatic acid, &c., and ultimately finishing with pure water. 



In this way the caoutchouc was purified without any altera- 

 tion of its original state. It now appeared in its state of mixture 

 with water perfectly white : portions of it left for a twelvemonth 

 over water underwent no change in that time, except coagula- 

 tion and a slight film upon the surface ; the rest was as miscible 

 with the water as at first, and when coagulated, equally elastic. 

 The sap or the washed caoutchouc is much more easily pre- 

 served in the diluted than in the concentrated state. 



It produced no particular appearance with the solutions of 

 iron or other metals. 



When evaporated, either on paper, in a capsule, or other- 

 wise, the caoutchouc was left in its elastic state, and perfectly 

 unaltered, except with respect to purity. When put on to ab- 

 sorbent surfaces, as bibulous paper, chalk, or plaster of Paris, 

 the water was rapidly abstracted, and the caoutchouc almost 

 immediately united into a mass, retaining the form of the thing 

 on which it was cast. In this way Mr. Hancock has made 

 beautiful medallions with the sap. Poured on to a filter, the 

 water passes through, and the caoutchouc coagulates. 



When aggregated in any of these ways, the caoutchouc ap- 

 pears at first as a soft white solid, almost like curd, which by 

 pressure exudes much water, contracts, becomes more compact, 

 has acquired elasticity, but is still soft, white and opake. It 

 also attains this state without pressure, if time be permitted 

 for the water to evaporate. The opacity belonging to it is not 



