When the silk is taken out of this second water, they wring it hard with a wooden peg to press out all the soap and water; after which they shake it to untwist it, and separate the threads. It is then suspended in a kind of stove constructed for that purpose, in which sulphur is burning, the vapour of which gives the last degree of whiteness to the silk. Woollen cloths are sometimes bleached by simply scouring them with soap and water after the operation of the fulling mills, and sometimes by sulphuric acid gas, which is effected as follows: - The stuffs are first well washed and cleansed in river water, and then put upon poles to dry. When half dry, they are exposed to the vapour of burning sulphur, or sulphurous acid gas, in a very close stove; the gas gradually adhering to the surface of the stuff, renders it beautifully white. An improvement upon this method is to condense the sulphurous acid in water, and immerse the stuffs therein; by which means the acid acts more equally over the whole surface, than when in the state of gas. The gas may also be obtained by digesting sulphuric acid upon chopped straw, saw-dust, or other carbonaceous matter, in a retort, and the gas may be condensed by an apparatus similar to that used for condensing the chlorine gas.

High pressure steam has been lately employed instead of chlorine for bleaching cloths. It is said that this method of bleaching has long been practised in the east, but Chaptal is the first writer who recommended it to the European bleacher; and Mr. S. Wright has taken out a patent in this country for an apparatus for washing and bleaching upon this principle, which apparatus is represented in the annexed engraving. The goods to be bleached are first packed closely into a conical vessel, through which the steam is caused to pass for a while; the steam is then made to force an alkaline solution through the goods, to remove the impurities and colouring matter (which operation is repeated as often as may be necessary); hot water is next impelled through the goods to remove all the alkaline matter; and, lastly, steam of a high pressure is forced through to expel the water, by which the goods are left in nearly a dry state, and perfectly clean. a is a copper vessel, formed as frustrum of a cone, at the lower part of which is a perforated false bottom, or grating, and below this the real bottom, from which a pipe descends.

The articles to be operated upon having been previously laid in water and rubbed with soap, are to be closely packed in this vessel, the lid of which is then to be screwed down and rendered steam-tight at the junction. In the diagram this vessel is represented enclosed in a jacket, to prevent the radiation of heat;

Bleaching 177Bleaching 178

B is a vessel (also of copper, as well as the other vessels and tubes represented), containing soap and water, or the usual alkaline solutions of pearl-ash, soda, etc.; C is a pipe leading from a steam boiler, through which is introduced steam at a pressure of 50 lbs. on the inch, which is first to be gradually admitted into the apparatus, by partially opening the stop-cock a, when it passes into the vessel A, where it is allowed to act upon the goods therein deposited, for half an hour; after which the cock a may be completely opened, and the full force of the steam allowed to operate, first opening the cocks b, c, d, e, when the steam will pass up the pipe D into the vessel B containing the alkaline solution. The pressure of the steam upon the surface of the liquid in this vessel will now cause it to descend through the pipe E into the vessel A, and herein the steam: continuing to press, will force the alkaline liquid through the goods, saturating every part, and carrying the dirt and other impurities to the bottom, the liquid passing off through the pipe F into the receiver G underneath.

The pressure of steam is next employed to refill vessel B with the discharged alkaline quor; for this purpose the cocks b, c, d, e, are to he closed, and the cocks f and g, to be opened; the steam will now pass down the pipe H, and operate with its full force upon G, thereby forcing the liquid up the pipe l l again into B, from whence it is again forced through the goods in the vessel A, repeating the operation as often as may be necessary, in order perfectly to cleanse them. The dirt, and other impurities, being removed, the next process is that of rinsing, which is effected by closing the cocks b, c, d, e,f,g, and opening those at h, i, A, when the steam from C passes up the pipe K into the vessel L, which is filled with clean hot water; the full pressure of the steam being now transferred to the surface of the hot water, forces it through the pipe M and through the goods in the conical vessel A, carrying away all the alkaline and other impurities through the pipe N into the vessel O.

The hot liquor in O is now to be returned into L, by closing the cocks i, k, h, and opening those at l, m, when the steam passes down the pipe P, and forces the liquor contained in O, up the pipe Q Q, again into L, for the renewal of the operation; this part of the process being also repeated as many times as may be deemed desirable, which will depend upon the condition of the goods. The next stage of the process is drying, which is effected by closing all the cocks, except those at d, e, and allowing steam, at a reduced pressure, to pass direct from C into the vessel A again, by which all the water is driven out from the goods, leaving them nearly all in a dry state, the steam passing off through the pipe F, and escaping at R. In this part of the process it is necessary to observe that steam should not be employed at a greater pressure than 20 lbs. on the inch, and that its action should not be prolonged beyond the time necessary to drive off the water. For the bleaching of piece goods, in lieu of the circular-sided vessel A, the patentee recommends one with straight sides, diminishing downwards; in this vessel the goods having been carefully folded are to be closely packed, and, in addition to the steaming and washing, by means of alkaline solutions, currents of cold air, produced by a blowing machine, are to be admitted through the pipe S, which, it is said, greatly assists in whitening the fabric.