892 BLEACHING 



M. Hoard. Tho alkalis, or alkaline salts, act in a marked manner upon the varnish 

 of silk, and effect its complete solution ; the prolonged agency oven of boiling water 

 or soap and water destroys the brilliancy of silk. It would appear, however, that 

 the Chinese do not employ this method, but something that is preferable. Pro- 

 bably the superior beauty of their white silk may be owing to the superiority of their 

 raw material. 



Tho most ancient method of scouring silk consists of three operations. For the 

 first, or the ungumming, thirty per cent, of soap is dissolved in clean water at a 

 boiling heat ; then the temperature is lowered by the addition of a little cold water, 

 by withdrawing the fire, or at least by damping it. Tho hanks of silk suspended 

 upon horizontal poles over the boiler are now plunged into the soapy solution, kept at 

 a heat somewhat under ebullition, which is an essential point ; for, if hotter, the soap 

 would attack the substance of the silk, and not only dissolve a portion of it, but de- 

 prive the whole of its lustre. The portions of the hanks plunged in the bath get 

 scoured by degrees : the varnish and the colouring-matter are removed, and the silk 

 assumes its proper whiteness and pliancy. Whenever this point is attained, the hanks 

 are turned round upon the poles, so that the portion formerly in the air may be also 

 subjected to the bath. As soon as the whole is completely ungummed, they are taken 

 out, wrung by the peg, and shaken out ; after which the next step, called the boil, is 

 commenced. About 25 Ibs. or 35 Ibs. of ungummed silk are enclosed in bags of coarso 

 canvas, called pockets, and put into a similar bath with the preceding, but with a 

 smaller proportion of soap, which may therefore be raised to the boiling-point with- 

 out any danger of destroying the silk. The ebullition is to be kept up for an hour 

 and a half, during which time the bags must be frequently stirred, lest those near 

 the bottom should suffer an undue degree of heat. The silk experiences in these two 

 operations a loss of about 25 per cent, of its weight. 



Tho third and last scouring operation is intended to give the silk a slight tinge, 

 which renders the white more agreeable, and better adapted to its various uses in 

 trade. In this way wo distinguish the China white, which has a faint cast of rod, the 

 silver white, the azure white, and the thread white. To produce these different 

 shades, we begin by preparing a soap-water so strong as to lather by agitation ; we 

 then add to it for the China white a little arnotto, mixing it carefully in ; and then, 

 passing the silk properly through it, till it has acquired the wished-for tint. As to 

 the other shades, we need only azure them more or less with a fine indigo, which has 

 been previously washed several times in hot water, and reduced to powder in a 

 mortar. It is then diffused through boiling water, allowed to settle for a few minutes, 

 and the supernatant liquid, which contains only the finer particles, is added to the 

 soap bath, in such proportion as may be requisite. The silk, on being taken out of 

 this bath, must be wrung well, and stretched upon perches to dry ; after which it is 

 introduced into the sulphuring chamber, if it is to be made use of in the white state. 

 At Lyons, however, no soap is employed at the third operation ; after the boil, the 

 silk is washed, sulphured, and azured, by passing through very clear river-water 

 properly blued. 



The present practice in the silk-works in Lancashire is as follows : 



Tho Italian silk arrives in this country with a little soap in it, put in by the 

 throwsters there, amounting to one drachm to a pound of silk. It is received here in 

 hanks, and bleached in that state. The hanks are hung on sticks or small poles, about 

 three pounds of silk being on each stick. The sticks being laid across a vessel, the 

 silk hangs down, and in this way may be immersed in any liquid. The treatment of 

 silk is then much more tender than that of cotton. 



1. Tho hot lather is made with 3 Ibs. of soap in 50 gallons of water ; to this is 

 added 1 Ib. of soda crj'stals. The silk is kept in this lather at a temperature of from 

 175 V> 190 F. for three-quarters of an hour. It is then wrung or dried in the hydro- 

 extractor (called hydro or whizzer in Lancashire works). 2. It is then, for the pur- 

 pose of straightening it, rolled on a cocoa-nut roll-pin 4 in. in diameter, a little turn 

 being given it occasionally, by the finger and thumb, to prevent entangling. 3. It is 

 then put into bags of one yard square. The hanks are laid flat, and the bags stitched 

 down. In this state they are boiled for 3 hours, using for the same amount of water 

 as before, 3 Ibs. of soap to 20 Ibs. of silk. 4. The silk is then washed or moved about 

 by the hand in a cistern one yard wide and one deep, retaining as much soap as will 

 make a pretty permanent lather. To this there is generally added a small quantity 

 of archil, about ^ oz. to 4 Ibs. of silk. 5. It is then dried in the hydro-extractor. 

 6. It is then straightened and sulphured. The sulphuring is done in a small apart- 

 ment, which should bo very high. The size is frequently 10 feet square by 20 in 

 height. The silk is hung up in it, and 4 Ibs. of sulphur for cacli 40 Ibs. of silk aro 

 put on the floor and set fire to. The room is closed as well as possible, and the silk 

 js allowed to remain 4 hours. This is the bleaching, and it requires now only to be 



