The whitened pyroxyline is put into boxes lined with filtering cloths, and then submitted to mechanical drying. On being taken from the hydro-extractor, the material still retains about 40 per cent, of water, and is found to be in a state fit for the preparation of celluloid. It is then passed through a mill having . metallic runners, first alone, and afterwards mixed with the proper quantity of camphor (which has been first rolled), and with colouring matters if it be proposed to make opaque celluloid. After a dozen successive grindings, the mixture is moulded in a metal frame, by hydraulic pressure, so as to give slabs, that are arranged and pressed between 10 to 12 sheets of thick bibulous paper. The water in the mixture is then gradually absorbed by the paper, the latter being renewed 12 to 15 times. The slabs, thus dried and reduced to a thickness of about ^ in., are broken up between bronze cylinders armed with teeth. The pieces are allowed to macerate for about 12 hours with 25 to 35 per cent, of alcohol of 96°, and then the colouring matters soluble in alcohol are added, if it be proposed to have transparent coloured celluloid.
The mixture is then passed through the rolling-mill, the cylinders of which are heated to about 122° F. (50° C). The operations are performed upon 20 to 28 lb. at once. The rolling takes 25 to 35 minutes, and terminates when the material has become homogeneous. There is then obtained a sheet of about J in. in thickness, which is cut into pieces of 23 1/2 by 31 1/2 in. The latter are superposed on the table of a hydraulic press in a metallic box having double sides and being tightly closed, and allowing the heating to be done by a circulation of hot water. The box is heated to 140° F. (60° C.) during the whole duration of compression, which lasts about 4 hours. At the end of the operation, a current of cold water is passed into the box, the pressure is removed, and there is obtained a very homogeneous block of celluloid about 5 in. thick. The blocks are taken to the planing machine, and shaved into sheets varying from 0.008 to 0.12 in. in thickness, according to the purpose for which the product is designed. These sheets are next placed in a ventilated stove, heated to 131° F. (55° C), where they remain for 8 days to 3 months, according to their nature and thickness.
In this description it has been only a question of celluloid of a uniform colour, either transparent or opaque, imitating pale tortoise-shell, coral, ebony, turquoise, etc. When it is desired to obtain a product to imitate amber, jade, spotted tortoise-shell, etc, each of the ingredients, of uniform colour, which is to compose the material, is prepared separately, and then mixed, to be afterwards united by pressure.
(20) A new compound, said to be fireproof, and suitable as a substitute for ivory, is thus made: - A solution is prepared of 200 parts of casein in 50 parts of ammonia and 400 of water, or 150 parts of albumen in 400 of water. To the solution the following are added: quicklime, 240 parts; acetate of alumina, 150 parts; alum, 50 parts; sulphate of lime, 1200 parts; oil, 100 parts. The oil is to be mixed in the last. When dark objects are to be made, 75 to 100 parts of tannin are substituted for the acetate of alumina. When the mixture has been well kneaded together and made into a smooth paste, it is passed through rollers to form plates of the desired shape. These are dried and pressed into metallic moulds previously heated, or they may be reduced to a very fine powder, which is introduced into heated moulds and submitted to strong pressure. The objects are afterwards dipped into the following bath: - Water, 100 parts; white glue, 1 part; phosphoric acid, 10 parts. Finally, they are dried, polished, and varnished with shellac.
(21) Any form of cellulose is the basis. Sulphuric acid, sp. gr. 1.84 to to 1.85 (75 parts), is placed in a receiver, with 25 parts commercial nitrous acid; a saturated solution of peroxide of nitrogen in nitric acid, sp. gr. 1.420, is retorted a little below 132° F. (55 1/2° C), the fumes passing into the sulphuric acid until it is saturated by them. The cellulose is immersed in this acid, 11 lb. of cellulose to the gallon, then taken out and left to stand an hour, then thoroughly washed and dissolved in alcohol (sp. gr. 0.920) 75 parts, and coal-oil 25 parts, in the proportion of 11 lb. solvent to 11 lb. fibre.
(22) In making articles of artificial ivory, the greatest difficulty hitherto has been that, in order to gain the necessary firmness, a large percentage of the binding substance had to be used, and hence only dull-coloured articles could be produced. Recently J. S. Hyatt has produced a substance in which only very little gum or other cementing material is used, so that, without detriment to its durability, the finished article may still have a pure white colour. This result is arrived at by grinding up any suitable inert matter with a solution of a proper cement. The cement solution is then expressed, the residue is dried and ground, and the powder thus obtained is heated and pressed into moulds. The most suitable inert matter found is oxide of zinc, and the best cement is shellac, orsome other similar vegetable substance. A solution of NH, forms the solvent. Hyatt first dissolves 8 parts shellac in 32 parts NH2 sp. gr. 0.995, by thoroughly mixing the two at a temperature of 99° F. (37 1/2° C.) for 5 hours in a rotating cylinder. 40 parts of oxide of zinc are now mixed by hand into the thin syrupy solution, and the mixture is well ground in a colour-mill. The NH2 having served its purpose, is now driven off by heat, or by exposing the mixture on glass plates for a long time to the air.
The residue, consisting merely of dry shellac and zinc oxide, is again finely powdered, and the powder thus obtained is pressed into the moulds with a pressure of about 2000 lb. per sq. in., and at a temperature of 257° to 280° F. (125° to 137 1/2° C). If the article is to be coloured, the colour is added either to the solution just before the first grinding, or to the dry mass before the second grinding.