Page:Popular Science Monthly Volume 17.djvu/829

Rh full account of them in the manuals of chemistry. In this retort, the dry distillation of caoutchouc is being carried on, and in time very nearly the whole of the India-rubber will be converted into the mixture of oily hydrocarbons, only an insignificant carbonaceous residue remaining in the retort. The mixture of volatile hydrocarbons, often referred to as caoutchoucine, forms a very good solvent for caoutchouc and certain resinous bodies.

India-rubber is subject to two kinds of deterioration and decay. In one instance it tends to become soft, and loses its elasticity, while in the other it becomes friable, yellowish, and resinous in its nature. Examples of each kind of deteriorated rubber are on the table, and you will notice that, in the case of this specimen, we have a well-marked instance of both kinds of deterioration going on side by side. The last-mentioned kind of deterioration has been clearly and indubitably traced to an oxidation of the caoutchouc. This oxidation is tolerably rapid when the caoutchouc exists in a finely divided state, and when it is exposed to damp at the same time; but the alternate damping and drying of the caoutchouc tends more toward its rapid oxidation than does a continual state of dampness. The resinous matter resulting from the oxidation of caoutchouc has been carefully studied by Spiller, who found that a sample of felt, originally composed of cotton fibers and India-rubber, had become so far changed during six years as to contain no trace of caoutchouc; but in its place he found a resinous substance resembling shellac. This resinous body, of which a sample is before you is easily soluble in alcohol, and also dissolves in benzole. Alkalies dissolve it readily, and acids precipitate it from the alkaline solution. It contains 27·3 per cent. of oxygen.

The conditions under which the softening of the India-rubber takes place are not so well understood, but there is some reason to believe that this is due to incipient oxidation.

Ozone oxidizes caoutchouc with extreme rapidity, as Warren pointed out in 1877, and I have arranged a simple experiment to illustrate this fact. Through the open end of this glass passes a slow stream of air which has been slightly ozonized; that is to say, a portion of its oxygen has been converted into ozone. When the stream of ozonized air is allowed to impinge on a surface of India-rubber, you see that the surface is instantly corroded and roughened. Again, note the effect of allowing: the ozonized air to act on the surface of a distended caoutchouc balloon—you see that it bursts immediately. I should mention, by the by, that in the case of these balloons the caoutchouc is slightly vulcanized, but the action of ozone on vulcanized India-rubber is similar to its action on the unvulcanized material.

It is extremely probable that the rapid deterioration of caoutchouc, which is known to take place under conditions which are not perfectly understood, is frequently due to the corrosive and oxidizing action of ozone.