Instead of evaporating the solvent used in making the celluloid, it may be removed by precipi tating the pyroxyline by means of water, mineral naphtha, &c. There is thus obtained a semi-solid mass, containing a small quantity of the solvent, which is passed through grinding rolls or other disintegrating machinery, and then worked up as usual. The celluloid is placed in a vessel taining a revolving agitator or beater, together with water or mineral naphtha iu the proportion of l lb. of celluloid to 1 qrt. of liquid, and the agitator is set in motion. After a short time, the cellu loid is lot out in a eurd-liko form, and submitted to pressure (not excessive), to separate the liquid. It is convenient to plaeo it in a vessel of cylindrical form, and about 12 in. in diameter, provided with a movable and perforated bottom, covered with several layers of wire gauze. This is filled with the eurd-like celluloid, upon which a plunger is forced down, and a cheese-like block is produced. This is rolled down between rollers heated by stea,m, as already described, and any pigment, &c., is worked in by them at the same time, the mixture being passed through and through till perfected.
The solvent used is preferably mineral naphtha, as free from smell as possible. The solvent taken up by the liquid is recovered by distillation, if water has been used ; but in the case of naphtha, the greater part will separate on standing, and may then be decanted off.
In order to make celluloid in imitation of pearl, fish-seales are mixed with the dissolved pyroxy line, and a pearly-lustrous material is thus produced. To form a thiu veneer of artificial pearl, one part of this material is mixed with 100 parts of pyroxytine. The latter is first ground wilh a solvent and oil to a doughy consistency, the peozly compound is then added, the solvent is separated, and the celluloid is worked up in the ordingy way. But when the celluloid is required in a semi-fluid con dition, the solvent must be increased instead of removed, and a much larger proportion of the pearly inaterial will be needed. The best lustre produced is that made in France, from the seales of the whiting. Li producing a coloured celluloid, preference should always be given to dyes--especially aniline—rather than pigments. The brightest and most delicate colours may be imparted.
To manufacture celluloid so as to resemble ivory, the following plan is adopted. The celluloid is made without any colouring matter, and is kept as clean and white as possibte ; when in Et dough like state, it is rolled into sheets ,211. in. thick. Maintinie another celluloid RI propezed, containing carbonate of strontia in the proportion of oue part to about 200 parts of pyroxyline, and this also is rolled into sheets. Those sheets are placed alternately one over another to produce any desired grain. A good plan is to lay a transparent and an opaque sheet one over the other, and roll them
up together, then take the roll and twist it, pass it through heated rollers and roll it down into a slab, for cutting knife handles or whatever may be required.
In working white of light-eoloured celluloids, or those in imitation of pearl or ivory, it is neces sary that poreelain or glass vessels should be used in its manufaetnre as far as possible, and the rollers through which it is passed must be eovered with platinum, as otber metals are acted upon by the eelluloid. A coating of platinum -,%.6 in. thick will be very durable.
For producing a white celluloid, without unduly increasing its specific gravity, the dissolved pyroxyline and other ingredients are mixed with white starch, either from wheat, rice, potatoes, &c., or with arrowroot, tapioca, or other amylaceous substance, or with wheat flour, or with eotton, ground and bleached.
To remove the solvent remaining in the celluloid, which imparts a slight odour to articles inade of it, and renders them liable to shrink in course of time, such articles are seasoned while in a partially manufactured state, by soaking them in a liquid which will dissolve out the solvent without affecting the pyroxyline, such as bisulphide of carbon, ehloride of nine, or benzol. The articles so soaked are afterwards placed in a vessel from which the air is exhausted, and the curing-, liquid is thus drawn out, condensed, and recovered.
The process employed for ma..king billiard balls is as follows. To 100 parts of pyroxyline, dis solved, ground, and strained as usuat, are added 300 to 500 parte of the usual solvent—aleohol 100 parts, naphtha 50 parts; 100 to 150 parts of arrowroot or starch ; and 50 to 100 parts of the best zinc-white. The solid matters are added to the plastic solution of the pyroxyline, and the whole is placed in a closed rolling or grinding apparatus, the rollers being heated by steam as described, and the compound is ground up till most of the solvent is driven off. The latter is reeovered by convey tog it through pipes to a Liebig's condenser. Tlae mass is now about as stiff as clay, and may be moulded or rolled, and plaeed in a warm place for seasoning. When well seasoned, the ball may be turned. When less specific gravity is required, it is best to employ as much amylaceous substances as poasible, they being lighter than the zinc. Ground and bleached eotton fibre may be ground up with the plastic) pyroxyline, in the proportion of 100 parts disintegmted cotton to 300 parts pyroxy line paste. When making coloured eelluloid with amylaceous substances or cotton, the colours should be added at the same time, and ground up with the other ingredients.