Page:Experimental researches in chemistry and.djvu/193

178 charcoal and compounds of carbon and hydrogen; it yields no ammonia by destructive distillation, nor any compounds of oxygen, and my experiments agree with those of Dr. Ure, in indicating carbon and hydrogen as its only elements. I have not, however, been able to verify his proportions, which are 90 carbon, 9.11 hydrogen, or by theory nearly 3 proportionals of carbon to 2 of hydrogen, and have never obtained quite so much as 7 carbon to 1 hydrogen by weight. The mean of my experiments gives, —

No means which have yet been discovered seem competent,when the caoutchouc has once been aggregated, to restore it toits pristine state. Previous to its aggregation it may be either scented or coloured. A solution of camphor in alcohol was added to water, so as to precipitate the camphor in a flocculent state; a little of this was added to some of the pure caoutchouc in water well agitated, and then coagulation caused by heat or absorption; the caoutchouc obtained was highly odorous.

In the trials made to give it colour, the body colours werefound to answer best—indigo, cinnabar, chrome-yellow, carmine, lake, &c., were rubbed very fine with water; then mixed well with the pure caoutchouc, in a somewhat diluted state, and coagulation induced either upon an absorbent surface or otherwise. Perfectly-coloured specimens were thus obtained.

The aqueous liquid obtained either by letting the sap stand for some time, or by the first and second washing, was of a brown colour, bitter, acid to litmus in consequence of the presence of acetic acid, due apparently to spontaneous changes in the substances present. It was difficult to filter. Being boiled, acid vapour rose, a precipitate fell to the bottom, and now the solution (a) became clear, either by standing or filtration, and could be separated from the solid matter.

The precipitate or substance thus obtained was dark brown, glossy and brittle, much heavier than water, not soluble in alcohol, ether, water, essential or fixed oils. Weak solution of alkali dissolved it, forming a deep brown solution, precipitable by dilute muriatio acid. It burnt upon platina-foil, like animal matter, with flame, leaving a bulky charcoal. When, heated in