THE INDIA-RUBBER INDUSTRIES. 811 



body, less soluble in benzole than unaltered caoutchouc ; and, it is quite 

 possible to obtain a photographic print by exposing a film of India- 

 rubber under a negative, and then dissolving away, by means of benzole, 

 those parts on which the light has not acted. Here is such a photo- 

 graph made by Mr. Woodbury. I now project it on the screen, so 

 that you may all see it. It is generally a discreet thing to keep India- 

 rubber where it will not be exposed to the prolonged action of a power- 

 ful light, although there are cases in which exposure to light is a use- 

 ful aid to the process of vulcanization. India-rubber is, to a certain 

 extent, porous and cellular in its texture, as may be seen by a micro- 

 scopical examination of a thin section. Again, if a thin leaf of caout- 

 chouc is boiled for a long time in water, it absorbs a considerable pro- 

 portion of this liquid. You see that this piece of caoutchouc has be- 

 come quite milky and translucent from the absorption of water, and it 

 probably holds, at the present time, as much as ten or fifteen per cent, 

 of water. The amount absorbed may, in some cases, rise as high as 

 twenty-five per cent. In a similar manner alcohol is absorbed by 

 India-rubber, more readily than is the case with water. 



Now, we pass on to a more important matter, namely, the action 

 of such liquids as benzole or coal-naphtha on caoutchouc. Here are two 

 cubes of Para rubber, each being three eighths of an inch across the 

 face. One of these I will preserve as a pattern, and the other I will 

 suspend in a bottle containing benzole. The cube suspended in the 

 benzole will immediately begin to swell, and will continue to do so 

 until it has attained a bulk about one hundred times as large as its 

 original size. During the time that the cube is swelling in the benzole, 

 a certain proportion of the caoutchouc will become dissolved out and 

 incorporate itself with the bulk of the solvent. Now, as a matter of 

 fact, every kind of natural India-rubber contains tw r o distinct modifica- 

 tions of caoutchouc, one of which tends to swell up in such a liquid as 

 benzole, while the other dissolves and forms a true solution. The fii'St 

 mentioned of these bodies may be referred to as the fibrous constituent 

 of caoutchouc, while the second may be spoken of as the viscous con- 

 stituent. The proportions in which these two bodies occur in raw rub- 

 ber vary extremely, Para rubber, of good quality, containing only a 

 small proportion of the viscous constituent, while African tongue, on 

 the other hand, consists principally of the viscous modification of caout- 

 chouc. The viscous constituent of caoutchouc is the agent princi- 

 pally concerned in the joining together of freshly cut edges of India- 

 rubber ; and, as we proceed with the study of caoutchouc, we shall see 

 that, under certain conditions, the fibrous caoutchouc can be more or 

 less perfectly changed into the viscous form. The treatment of the 

 juice of the India-rubber trees is often of such a nature as to greatly 

 deteriorate the caoutchouc obtained ; a considerable proportion being 

 thus changed from the fibrous to the viscous condition. This kind of 

 injury to the caoutchouc can be obviated by coagulating the milky 



