Page:Encyclopædia Britannica, Ninth Edition, v. 3.djvu/832

sary to satisfy the eye, whereas in print-bleaching the material must be rendered chemically pure, otherwise the colours in the subsequent printing process would be dull and blotchy. The print bleaching must therefore be more thoroughly done than the other ; but as the processes arc generally the same, it will be sufficient to indicate the points of difference in the various stages through which the material in both cases passes. A process preliminary

to bleaching is.

FIG. 4. Section of Singe Stove.

Singeing.—Gray calico a3 received from the looms is generally in lengths of 37 and 50 yards. A large number of these, sometimes as many as 1000, measuring more than 20 miles in length, are sewn into a continuous web. At the extremities of each owner s lengths, the name of the firm, or some distinguishing mark, is either stamped on in tar, or marked by means of coloured threads. These long lengths are then submitted to the operation of singe ing, which lias for its object the removal of the downy pile and short threads from the surface of the cloth, which would interfere with the appearance of finished white goods, and with the uniformity and sharpness of patterns in the case of prints. Several methods of accomplishing this have been employed, but that most commonly used is the system of plate singeing illustrated in fig. 4. A pair of singe-plates, a and b, made of thick bent sheets of copper, are mounted over the flues of a fire sufficient to raise a white heat. The plate b is most highly heated, a being at the end of the flue furthest removed from the fire. The cloth enters over a rail a, and in passing over the plate a is thoroughly dried and prepared for the singeing it receives when it comes to the highly-heated plate b. A block d, carrying two rails in the space between the plates, can be raised or lowered at pleasure so as to increase or lessen the pressure of the cloth against the plates, or, if necessary, to lift it quite free of contact with them. The system of plate singeing is found generally sufficient in practice, but the caking of paste and dirt on the plates from the cloth as it passes over them, and variations in the heat of the plates, often lead to irregularities in singeing. A combination of plate and gas singeing is frequently employed to over come the deficiencies of plate singeing alone. In this case the cloth is passed first over an ordinary plate, and then on to another, along the ridge of which is a long narrow slit, which allows the issue of a gas flame produced from coke burning immediately under it. By this means long loose threads are more effectually burned off than in plate singeing, and a more uniform heat is applied to the gray cloth. Fig. 5 is a sectional view of a very efficient singe ing apparatus introduced by Messrs Mather and Platt. The figure represents the first half of the machine, the second portion being precisely similar in arrangement. The singeing in this case is accomplished by the burning of a mixture of coal-gas and atmospheric air admitted by a pipe a, and driven by a fan Diast to the burners b, b, which are regulated by stop-cocks. The mixture burns with an intense heat and a blue smokeless flame. The cloth is carried by a series of rollers to the gas jets, and in passing over the rollers c, c, c, c the one side of the cloth impinges laterally four times against the flame, which is never permitted to pass through the fabric, but only shaves its surface. The back is thus singed in the first portion of the apparatus, and being turned over on roller d it is carried forward to another pair of jets, where, being thoroughly dry, the face side of the cloth is completely singed by going over exactly the same course through which the back is carried in the first part. By an arrange ment not shown in the illustration, the attendant of the machine can instantaneously lower the gas burners by a treadle movement in case of any stoppage or accident, and thus prevent the cloth from being burned. With a proper pressure of gas this machine singes at the rate of GO yards per minute.

5. Gas Singeing Apparatus.

At this stage the cloth lias now in addition to the brown coloured incrusting substance and the resinous material proper to the fibre, a dark-coloured carbonized surface, caused by the singeing process, the weaver s paste or dressing, tallow or other fat introduced in the pro cess of weaving, and the accumulation of dirt which the handling of weavers and others may have produced. The object of the subsequent processes is to wash out the mechanical impurities and resinous substances from the cloth, to render soluble by chemical agencies such as are otherwise insoluble in water, and to oxidize the colour ing matter of the cotton by the chloride of lime as already explained.

Liming.—In some cases it is the practice immediately

after singeing to steep the pieces in water and pile them up wet for a night, in order to loosen and partly ferment the weaver s paste, which is then in large part removed by washing in a machine to be subsequently described. The " gray-backs " which have been used in calico-printing have always to be thus steeped, and at one time it was the practice to leave the cloth so long in this steep that it acquired a most offensive odour. This preliminary steeping and washing facilitates the percolation of the liquor through the fabric in the process of boiling, but notwithstanding this advantage it is generally dispensed with, and the goods pass direct from the singeing to the liming process. The pieces are formed into a loose coil or rope by being passed through circular rings of glass or pottery called " pot-eyes," and worked up and down several times in a strong milk of lime, in order that the whole may be uniformly and thoroughly impregnated. The arrangement for liming will be understood from fig. 6, which is a sectional view of a " squeezer," an apparatus used repeatedly in subsequent operations as well as in this of liming. . The cloth passes up and down as indicated by the arrows, dipping several times into the solution, and before passing finally on to

the kiers for boiling it is slightly " nipped : between tho