The discharge pipe is passed through an equalizing warm-water vessel, which keeps it sufficiently warm to prevent the material in contact with the inner surface cooling faster than the central portion, as the unequal cooling, and consequent unequal consistency, of the different portions of the material would cause the central and softer portion to move faster than the outer and harder portion, thus destroying the homogeneity of the mass, and rendering the surface rough and broken. The soluble pyroxyline is first comminuted in a wet condition, and the excess of water is pressed out. The camphor and colours, as required, are then thoroughly incorporated with it by the mixing rollers. The compound, thus prepared, is formed into cakes by means of a mould and follower, the bottom of the mould being made separate, and serving to transfer the formed cake to the pile. These cakes are preferably made about 12 in. square, and 1/4 to 1/2 in. thick; it would be difficult to properly absorb the moisture from thicker cakes. These are laid up in a pile with layers of blotting-paper between them, and are then placed in a hydraulic press to remove the water as far as necessary.
During this process, the compound is protected from the air, to prevent evaporation of the camphor and to avoid the chance of ignition. The rapidity with which this drying is effected ensures great saving of time and space. The dried material is ready for conversion into celluloid, for which purpose it is transferred, with the solvent, to the converting cylinder. The heat from the steam-jacket surrounding the lower portion of this cylinder brings about the conversion of the pyroxyline to a homogeneous mass of celluloid, which is then forced through a discharge nozzle, constructed according to the desired form of the product, e.g. in bars or sheets, or directly into a mould of the article to be manufactured.
(17) The use of various solvents and combinations of solvent materials has been attempted or proposed; e.g. a mixture of camphor and oils in about the following proportions, viz.: - Camphor, camphor oil, or liquid camphor...... 20 pts. by wt.
Oil, such as castor or linseed, before or after boiling............ 40 „ „
Pyroxyline (soluble) .... 40 „ „
These will give a consbtency suitable for covering telegraph wires, or for moulding or spreading. For material with greater or less flexibility, or greater or less fluidity, the proportion or character of the oil must be changed. In producing very hard or rigid material, it is preferable to use oils which will themselves harden by exposure to air, as those which have been boiled. Camphor may also be used in about equal proportions with hydrocarbons having a boiling point at 220° to 400° F. (l04°-204° C), or with alcohol or spirits of wine; or hydrocarbons in equal proportions with alcohol; or castor-oil in equal proportions with alcohol; or a distillate of a mixture of camphor-oil and hydrocarbons, or of camphor and bisulphide of carbon in conjunction with alcohol; or aldehyde, either alone or with alcohol. Either of these solvents -may be employed with the other ingredients in about the following proportions, to produce a semifluid celluloid: - Pyroxyline (soluble) .. 27 pts. by wt.
Castor-oil........... 27 „ „
Camphor............. 6 „ „
Either of the foregoing solvents............ 40 „ „
The consistency will depend chiefly on the proportions of the oil, as before.
(18) Parkes suggests the use of a solution of carbon tetrachloride and camphor, either alone or with gums, resins, oils, dyestuffs, etc. He also proposes to use carbon bichloride and camphor, when the solution takes place under the aid of heat and pressure. Camphor, too, is a good solvent when heated to its melting-point; at this temperature and under pressure, it dissolves the nitrocellulose as fast as it can be mixed with the melted camphor, until it forms a stiff mass. This mass, to which other substances may be added, can be rolled and pressed into moulds. To lower the melting-point, he adds oil, paraffin, turpentine, alcohol, benzol, ether, etc, whereby thinner solutions are obtained. Another powerful solvent for nitrocellulose can be made by conducting sulphurous acid gas through granulated camphor, or by dissolving camphor in sulphurous acid. A solution of camphor in benzol, of such quality that no unpleasant odour is left when the compound is done, works very rapidly with the aid of heat and pressure. Oils, gums, resins, and dyes can be added according to taste. Turpentine and camphor also dissolve it with heat and pressure very quickly.
(19) The pyroxyline is obtained from cigarette paper of very good quality. This paper, in rolls 13 in. in width and 33 to 35 lb. in weight, is unrolled mechanically and immersed in a mixture of 5 parts of sulphuric acid of 66° B., with 2 parts of nitric acid of 42° B., kept at a temperature of about 95° F. (35° 0.). The cellulose of the paper, after 12 or 15 minutes' immersion, becomes changed into nitro-cellulose, which is soluble in a mixture of alcohol and ether. The solubility is tested by a hasty trial. The product is then removed from the acid bath, the liquid is expressed from it, and it is thrown into water. After a preliminary washing, it is placed along with water in a pulp vat, and triturated for 2 1/2 to 3 hours in order to obtain a homogeneous paste. The pyroxyline then has to undergo bleaching, the operation being effected by the use of a solution of potash permanganate. When contact with this reagent has beea sufficiently prolonged, the excess of permanganate is eliminated by washing. Then the mass is treated with a solution of sulphurous acid in order to dissolve the oxide of manganese, and the operation is finished by a series of washings in water.