Rubber Solvents

Benzine is an excellent solvent for caoutchouc and gutta-percha. Caoutchouc or rubber, may also be dissolved in ether, carbon sulphide, naphtha, spirit of turpentine, and chloroform.

Solutions

(a) A mixture of 6 parts absolute alcohol with 100 of carbon sulphide; the latter is the real solvent, the alcohol has an indirect action. The quantity of solvent required depends on the consistency of solution required; if moderate heat is used, and the mixture is shaken, the whole dissolves, but a better solution is obtained for adhesive properties by using a large quantity of solvent, not shaking, but drawing off the clear glazy liquid. (b) For a small quantity, place 1 fl. dr. sulphuric acid and the same quantity of water into a phial bottle, and well shake together. Great heat is evolved. Allow to stand till cool; then add 2 fl. oz. spirits of turpentine, and shake well. Great heat will again be evolved, and the colour changed to deep cinnamon. Allow to stand for 24 hours, after which a strong dark sediment will have fettled at the bottom of the bottle. Pour off the clear liquor into another bottle, and add 1 1/2 dr. common rubber cut up into fine shreds, and then place it uncorked over a very gentle heat, and allow to boil slowly for 5 hours. At the end of that time the rubber should be perfectly dissolved.

It can be concentrated by longer boiling, or thinned by the addition of more turpentine.

Piecing Rubber

Make a long bevel on the ends to be joined with a sharp rough-edged knife and water, scrape the bevels rough with the edge of the knife, and when quite dry, give each a coat of rubber solution: say 1 oz. rubber not vulcanised to 5 oz. turpentine. When the first coat is dry, give it another, and when that is dry, put the two ends together.

Ebonite And Vulcanite

The only difference between these two articles is in the colouring materials used. These terms are applied to a compound of rubber and sulphur, exactly the same as the common elastic bands, the only difference being in the time and heat required to vulcanise or harden the compound. To prepare it as sold in the form of combs, the rubber is put into a masticator along with a proper proportion of sulphur, and when thoroughly mixed a sufficient quantity is put into a mould of the right shape made of plaster of Paris, or other material which will not combine with sulphur, and exposed in a steam boiler to a heat of 315° F., and a pressure of about 12 lb. to the inch for 2 hours. It is then removed from the mould, and finished, and polished exactly in the same manner as ivory. The application of heat as above without a steam pressure is sufficient to vulcanise or harden the compound, but the result is not always so satisfactory, as the material is liable to be porous if not compressed whilst hardening. Gutta-percha may be treated in exactly the same manner as rubber, and cannot be distinguished from it, but is rather more troublesome to work.

The vulcanite may be turned or carved in the same way as ivory, with the advantage that it may be moulded to the required form without the great waste which attends ivory carving. It is also much less liable to fracture. The smaller the proportions of sulphur in the rubber, and the lower the temperature used, the softer and more elastic will be the rubber. About 10 or 15 per cent. of sulphur, and a temperature of 270°-275° F. for 4 hours, will make an elastic rubber; 30 per cent. of sulphur and a temperature of 315° F. for two hours will make a hard vulcanite like ivory.

The reader is also referred to the article on "Indiarubber Manufactures " in Spon's ' Encyclopaedia.'