towards the bars. The two bars are so adjusted as to leave a very narrow slit between the cloth and the upper bar, whereby the caoutchouc solution is distributed evenly over the surface. The cloth is next suspended in a well ventilated apartment for a few days to dry, after which a second and a third coating are applied in a similar manner.

Two pieces of cloth, thus prepared and nearly dry, are brought evenly into contact with their caoutchouc surfaces face to face, and immediately passed between two wooden rollers with pressure, whereby the caoutchouc surfaces become strongly adherent. The cloth is lastly suspended until quite dry, and freed as much as possible from the disagreeable odour of the naphtha.

A fabric of a similar nature to the preceding has been lately substituted for leather in the fillet cards for the cotton and tow manufacturers. It consists either of several alternate layers of strong cloth and caoutchouc, or of two sheets of caoutchouc with a piece of cloth interposed, or of two pieces of cloth with an interposed sheet of caoutchouc.

From the extreme adhesiveness of the fresh surface of caoutchouc, the naphtha and turpentine solutions may often be employed with advantage as a cement. Thus a very thin layer of caoutchouc carefully applied to the back of a book is sufficiently adherent to bind the leaves together firmly, without the trouble of stitching or sewing. In the patented method of binding books by means of caoutchouc (invented by Mr. William Hancock) the sheets are folded in double leaves, and when properly arranged in a press, the caoutchouc solution is applied

three or four times to the back, one coating being dried previous to the application of the next. The band of cloth for the back and sides is then cemented to the book with the caoutchouc solution; after which, the boarding is completed in the ordinary manner.

Caoutchouc is the basis of one of the preparations known as Jeffrey's Marine Glue, which is formed by adding to a solution of one pound of caoutchouc in four gallons of crude naphtha, made in the cold with occasional agitation, shell lac or gum lac in the proportion of two parts by weight of lac to one part of the solution, and the mixture is heated and stirred in an iron vessel provided with a tap at its lower part. When the caoutchouc solution and lac are thoroughly incorporated, the mixture is drawn off by the tap while hot, and poured out on slabs to cool. When required for use, it is heated to about 250° Fahr., and applied as ordinary glue. As this cement is not liable to be softened by water, like common glue, it is very valuable for uniting pieces of wood, &c., which are to be submerged in water.

When caoutchouc is heated in a distillatory apparatus to a temperature considerably above its melting point, it is decomposed, and the greater part is resolved into a vapour, which is capable of being condensed into a mixture of several oily liquids, some of which are possessed of very remarkable properties. The mixture is generally known by the name of caoutchoucine.

The proper temperature at which the distillation should be performed is about 600° Fahr. A darkcoloured oily liquid distils over, to the amount of about

eighty-three parts from one hundred of caoutchouc, nothing remaining in the still or retort but charcoal and the dirt of the caoutchouc. The process of distillation is facilitated by mixing the caoutchouc with some of the liquid distilled at a previous operation, in the proportion of one part of the liquid to two parts of caoutchouc.

When the dark-coloured product of the first distillation is subjected to several re-distillations, it becomes limpid and colourless. By changing the receiver as the distillation advances, and the temperature of the boiling point rises, the liquids which constitute the mixture may be separated to a great extent through their great difference in volatility: the most volatile constituent boils at about 90°, and the least volatile at about 680°.

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The chemical composition of these oily liquids has been made the subject of investigation by Dr. Dalton, Dr. Gregory, Himly, and Bouchardat. cording to Himly, they are all composed of carbon and hydrogen in the proportion of five eqs. of carbon to four eqs. of hydrogen, which is the same proportion as exists in oil of turpentine. By careful rectification he obtained one liquid, the boiling point of which was constant at 339° Fahr., to which he applied the name caoutchine. Its specific gravity was 0.842. Another portion, which boiled at 97°, was found by Dr. Gregory to have very nearly the same composition as olefiant gas, that is, the same number of equivalents of carbon as of hydrogen. When this liquid was treated with sulphuric acid, it became black, evolved sulphurous acid, and on the addition of water yielded another oil of the

same composition, which boiled at a temperature above 428°.

By surrounding the receiver with a freezing mixture, Bouchardat obtained a liquid, the boiling point of which was below 32° Fahr., to which he applied the name caoutchène. This is supposed to be identical with one of the products of the destructive distillation of oil, recognised as a distinct substance by Mr. Faraday, having the same composition in one hundred parts as olefiant gas. Its specific gravity was so low as 0.654. After the more volatile oils distilled over, there remained behind in the retort a liquid, which has received the name of heveène, the boiling point of which was 599° Fahr. Its sp. gr. was 0-921. It was found by Bouchardat to have the same composition as caoutchène.

The mixture of these liquids, or caoutchoucine, is an excellent solvent of caoutchouc, and also when mixed with some strong alcohol, of the various resins, especially of copal, which it dissolves without the aid of heat. It readily mixes with oils, causing them to become more fluid, and as it evaporates quickly is found to be a useful vehicle in some cases for oil-paints. Mr. Barnard procured a patent in 1833 for its applications in the arts; but the low price of coal naphtha, compared with that of caout choucine, must prevent the latter from being largely employed as a solvent of caoutchouc.

The caoutchouc stoppers for bottles, for the manufacture of which a patent was obtained by Mr.

Brockedon, are made in the following

manner.

Wool,

cotton, or other fibrous material, is felted into a roll

of the diameter and length required, and to such a degree of hardness as will leave the stoppers sufficiently soft and elastic. The roll is then coated with a solution of caoutchouc (either in naphtha or turpentine), which is allowed to become nearly dry; and over the fresh surface of caoutchouc thus obtained is laid a piece of very thin sheet caoutchouc, the surface applied to the roll having been previously rubbed with the caoutchouc solution to cause it to adhere firmly. The roll is then cut into proper lengths for stoppers, and the ends are covered with caoutchouc in a similar manner.

The combination of the shreds and small lumps of crude caoutchouc into a large block, from which a sheet may be cut, is effected by attrition and compression. In one method, the caoutchouc is first cleansed by being cut into small pieces, which are washed with water, and dried on hot iron trays. The pieces are then laminated by being passed between two iron rollers, and washed at the same time by a stream of water. This operation is repeated so long as the caoutchouc retains any foreign matters capable of being removed by washing.

The caoutchouc is then introduced into a strong iron cylinder, the interior of which is furnished with projecting spikes. The line of the axis of the cylinder is traversed by a strong shaft of wrought iron, which is also furnished with projecting spikes. By the revolutions of the iron shaft, the cylinder being fixed, the caoutchouc becomes kneaded, or "ground" (as termed by the workmen), evolves considerable heat from the rapid expansions and contractions which it suffers, and aggregates into a single elastic lump.

VOL. II.

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