Pieces of indiarubber may be readily united by means of the pasty mass obtained by acting upon pure rubber by its appropriate solvents. These are: Sulphuric ether, coal-tar naphtha, bisulphide of carbon, caoutchoucin, benzine, and oil of turpentine. But as it is difficult to dissolve rubber satisfactorily on a small scale, and as the cement may be bought ready made at a cheap rate, it is hardly worth while to enlarge upon its preparation. Those who wish to try it will probably succeed best by cutting pure rubber (not that which has. been vulcanised) into very thin slices, boiling it in water so as to soften and expand it, and then digesting it in hot coal-tar naphtha, or oil of turpentine. Several days are required to effect the solution. When this cement is used for uniting pieces of rubber, the surfaces which are to be joined must be fresh; the surfaces should therefore be either pared with a knife or rasped with a file. They may then be coated with the cement, pressed firmly together, and exposed to a gentle heat for a few days.
For mending indiarubber shoes, boots, and apparatus where the regular rubber cement cannot be obtained, the following directions have been given: Cut 2 lb. indiarubber into thin, small slices; put them in a vessel of tinned sheet-iron, and pour over 12 to 14 lb. of bisulphide of carbon. For the promotion of solution, place the vessel in another containing water previously heated up to about 86° F. (30° C.). The solution will take place promptly, but the fluid will thicken very soon, and thus render the application difficult, if not impossible. In order to prevent this thickening, a solution of indiarubber and resin in spirits of turpentine must be added to the solution of indiarubber in bisulphide of carbon, and in such quantity that the mixture attains the consistency of a thin paste. The solution of indiarubber and resin in spirit of turpentine should be prepared as follows: Cut 1 lb. of indiarubber into thin, small slices; heat in a suitable vessel over a moderate coal fire, until the indiarubber becomes fluid; then add ^ lb. powdered resin and melt both materials at a moderate heat. When these materials are perfectly fluid, then gradually add 3 or 4 lb. spirit of turpentine in small portions, and stir well. By the addition of the last solution, the rapid thickening and hardening of the compound will be prevented, and a mixture obtained which fully answers the purpose of gluing together rubber surfaces, etc.
It is said that a good cement, that will render indiarubber in any form adherent to glass or metal, may be made as follows: Some shellac is pulverised, and then softened in 10 times its weight of strong ammonia, whereby a transparent mass is obtained, which becomes fluid after keeping some little time, without the use of hot water. In 3 or 4 weeks the mixture is perfectly liquid, and, when applied, it will be found to soften the rubber. The rubber hardens as soon as the ammonia has evaporated again, and thus becomes impervious to both gas and liquids. For cementing the rubber sheet, or the material in any shape, to metal, glass, and other such surfaces, this cement is strongly recommended.
Virgin or native indiarubber is cut with a wet knife into the thinnest possible slices, which are then divided by shears into threads as fine as small twine. A small-quantity of the shreds (say 1/10 of the capacity of the bottle) is then put into a wide-mouthed bottle, and the latter is three-fourths filled with benzine of good quality, and perfectly free from oil. The rubber almost immediately commences to swell, and in a few days, if often shaken, it will assume the consistence of honey. Should it be inclined to remain in undissolved lumps, more benzine must be added. Thinness may be corrected by adding more indiarubber. A piece of solid rubber no larger than a walnut will make a pint of the cement. It dries in a few minutes, and, by using 3 coats in the usual manner, leather straps, patches, rubber soles, backs of books, etc., may be joined with great firmness.
Indiarubber, 8 gr.; chloroform, 600 gr.; mastic resin, 150 gr. The indiarubber is dissolved in the chloroform, the mastic is added, and the whole is left to macerate for 8 days, that being the time necessary for the solution of the mastic. The cement is applied cold on a brush, and is used for joining glass.
Very finely-divided indiarubber is melted at a temperature of 392° F. (200° C.). As soon as fusion commences, 1/15 the quantity of tallow or wax is added, taking care to watch the heat and to stir without ceasing. When the mass is completely melted, lime, slaked and sifted, is added in small instalments, till it amounts to half the quantity of the indiarubber. The cement thus obtained is soft; if the proportion of lime be doubled, the cement will be harder, but still supple. When the compound has acquired a suitable consistence, the fire is withdrawn, and the preparation is finished. This forms a good cement for hermetically sealing vessels. It does not dry, and remains for a long time ductile and tenacious; but it may be made to harden if necessary, by adding 1 part of red lead to the quantities indicated.
For Vulcanised Rubber. Oil and sulphur: 1 of sulphur to 12 of oil gives a substance like treacle; 4 to 12 of oil a stiff substance like rubber. To be successful in making this compound, take an iron ladle, such as is used for the melting of lead, and fill it not more than ⅓ full, and place it over a clear fire. Owing to a quantity of water being held in the oil by the vegetable matter, it will begin to seethe, and, if not closely watched, boil over into the fire. After a little time it will subside, the surface remaining quite placid, with now and then little flickers of smoke flitting across the surface. Your sulphur must be either roll brimstone or the crude sublimed, i.e. not washed or treated with acid. If the first, finely powder it, and mix by degrees in the oil, stirring all the time until incorporated. (8) Guttapercha. To make gutta-percha cement, melt together in an iron pan 2 parts of common pitch and 1 of guttapercha; stir them well together until thoroughly incorporated, and then pour the liquid into cold water. When cold it is black, solid, and elastic; but it softens with heat, and at 100° F. (38° C.) is a thin fluid. I It may be used as a soft paste, or in a i liquid state, and answers an excellent purpose in cementing metal, glass, porcelain, ivory, etc. It may be used instead of putty in glazing windows.