One peculiarity of the machine consists in the waste system applied to the mould box. Steam or hot or cold water is sent into the latter through the conduit, L, starting from a junction between pipes provided with cocks. When the water contained in the box is in excess, it flows out through the waste pipes, G, which terminate in a single conduit. Owing to the branchings at T, and to the cocks of the conduits that converge at L, it is very easy to vary the temperature of the box at will. The warm or cold water or steam may be admitted or shut off simultaneously.
When first beginning operations, the wick is introduced into each mould by hand. The piston table is raised by means of the winch, and is held in this position through the engaging of a click with a ratchet on the windlass. A fine iron rod long enough to reach beneath the pistons and catch the end of the wick is next introduced. After this is removed, the wick is fixed once for all, and in any way whatever, to the top of the mould. This operation having been accomplished, the piston table is lowered, and the machine is ready to receive the stearic acid. The moulds are of tin and are open at both ends. In order to facilitate the removal of the candles, they are made slightly conical. When the candles have hardened, the ends are equalized with a wooden or tin spatula, and then the piston table is raised. At this instant, the jaws, B, are closed so as to hold the candles in place. The latter, in rising, pull into the mould a new length of wick, well centered. A slight downward tension is exerted upon the wick by hand, then a new operation is begun. During this time, the candles held between the jaws having become hard, their wicks are now cut by means of the levers, C, and they are removed from the machine and submitted to a finishing process.—Revue Industrielle.
A NEW ALKALI PROCESS.
In several former notes and articles in these pages, we have spoken of the severe crisis through which the old established, or "Leblanc," process has now for some years been passing. It is, in fact, pushed well nigh out of the running by the newer process, known as the "ammonia-soda" process, and would have had to give up the battle before now were it not for the fact that one of its by-products, bleaching powder, cannot, so far, be produced at all by the ammonia-soda works. The bleaching powder trade has thus remained in the hands of the workers of the Leblanc process, and its sale has enabled them to cover much of the loss which they are suffering on the manufacture of soda ash and caustic soda.
In brief outline, the old Leblanc process consists in the following operations: Salt is decomposed and boiled down with sulphuric acid. Sulphate of sodium is formed, and a large amount of hydrochloric acid is given off. This is condensed, and is utilized in the manufacture of the bleaching powder mentioned above. The sulphate of sodium, known as "salt cake," is mixed with certain proportions of small coal and limestone, and subjected to a further treatment in a furnace, by which a set of reactions take place, causing the conversion of the sulphate of sodium of the "salt cake" into carbonate of sodium, a quantity of sulphide of calcium being produced at the same time. The mass resulting from this process is known as "black ash." It is extracted with water, which dissolves out the carbonate of sodium, which is sold as such or worked into "caustic" soda, as may be required. The insoluble residue is the "alkali waste," which forms the vast piles, so hideous to look at and so dreadful to smell, which surround our large alkali works.
The sulphuric acid required for the conversion of the salt into "salt cake" is made by the alkali manufacturer himself, this manufacture necessitating a large plant of "lead chambers" and accessories, and keeping up an immense trade in pyrites from Spain and Portugal. The development of the alkali trade in this country has been something colossal, and the interests involved in it and connected with it are so great that anything affecting it may safely be said to be of truly national importance, quite apart from what technical interest it may possess.
The "ammonia-soda" process, which has played such havoc with the old style of manufacture, proceeds on totally different lines. Briefly stated, it depends on the fact that if a solution of salt in water is mixed with bicarbonate of ammonium, under proper conditions, a reaction takes place by which the salt, or chloride of sodium, is converted at once into bicarbonate of sodium, the bicarbonate of ammonium being at the same time converted into chloride of ammonium.
The bicarbonate of sodium settles out at once as insoluble crystals, easily removed, marketable at once as such, or easily converted into simple carbonate of sodium, and further into caustic soda, as in the ordinary "old" process. The residual chloride of ammonium is decomposed by distillation with lime, giving ammonia for reconversion into bicarbonate of ammonium, and chloride of calcium, which is a waste product.