Nux vomica, gamboge, caoutchouc, cardamoms, teak and other valuable woods and gums are among the natural products.
Under certain conditions, as when latex is allowed to stand or is centrifugalized, a cream is obtained consisting of the liquid globules, which may be washed free from proteid without change, but, either by mechanical agitation or by the addition of acid or other chemical agent, the liquid gradually solidifies to a mass of solid caoutchouc. The phenomenon therefore resembles the change known to the chemist as polymerization, by which through molecular aggregation a liquid may pass into a solid without change in its empirical composition.
The globules which furnish the cream gradually pass on standing into solid caoutchouc, a process which is facilitated by rapid stirring, or by the addition of an acid or other chemical agent.
If the latex is warmed or an acid, an alkali or astringent plant juice is added to it, " coagulation " usually takes place more or less readily, the caoutchouc separating in solid flakes or curds.
When exposed to air the latex gradually undergoes putrefactive changes accompanied by coagulation of the caoutchouc. The addition of a small quantity of ammonia or of formalin to some latices usually has the effect of preserving them for a considerable time.