Pfocefsfor Bkach'ing Raiv Silk. 3j 



is commonly longer than for the firft : it fometimes amounts to two, three, or even (ii 

 days, according to circumflances, particularly the temperature and the nature of the filk. 

 Silk which has been in the o\cn is in general more ditficult to bleach. 



When the filk has thus obtained its utmoft degree of whltenefs, the acidulated fpirit is 

 to be drawn oiF into a feparate ved'cl. This fluid is but flightly coloured, and may be ufed 

 again in the firft infufion of other yellow filk, with the addition of fis ounces more of ma- 

 rine acid. The receiving vefiel is to be removed, and another clean veflel fubftituted in its 

 place. The filk is then fprinkled with clean fpirit, and occafionally prefled down with the 

 hand. As foon as the fpirit of wine comes ofFabfoIutely colourlefs, a third infufion is to be 

 made by pottring upon the filk forty-eight pounds of the pure fpirit without acid, which is 

 to remain till the following day : it is then to be drawn otF, and referved for wafliing other 

 filk after the firft infufion. 



After the filk has been left to drain, and affords no more fpirit, it flill retains its own 

 weight of that fluid. This is recovered by the very fimple procefs of fprlnkling the filk 

 with a fmall quantity of very clear river-water at a time. While the water applies itfelf and 

 fubfides along the filk, it drives the fpirit of wine before it, fo that the firft portions which 

 flow from the tube are fcarcely diminifhed in ftrength. The addition of water is to be 

 continued until nothing but mere water comes off below. 



In this fituation the filk is found to be well bleached, but ftlll retains a portion of marine 

 acid f'jfficient to render it harfli to the touch, and after a time brittle. It muft be walhed 

 off with water. The beft method is to put the filk loofely into a coarfe woollen bag, which 

 is to be fecured loofely in another cloth Hke a fmall bed or pillow, then placed in a bafket 

 and left in a running ftream for five or fix hours ; but where the convenience of a flream 

 is wanting, the earthen pot containing the filk is to be covered with a clotli, and water 

 pumped through it for five or fix hours, or until that which ifliies from the lower aperture 

 gives no red colour to the tincture of tournfol. At this period the lower opening is to be 

 clofed and the vefTel filled with water, which muft be changed once or twice in twenty-four 

 hours. 



The time required for wafliing was occafionally abridged by parting fpirit of wine, or river- 

 water impregnated with a fmall portion of alkali, through the filk. The neutral fait thus 

 produced is in fad lefs adherent to the filk than the acid itfelf, but neverthelefs requires 

 to be wafhed off with a very large quantity of water. 



In thefe as in every other procefs relating to the filk, great care muft be taken to afcer- 

 tain that the water made ufe of contains no nitrous acid, which would infallibly occa- 

 fion imperfeflion of'colour, or fpots in the article. After this treatment the filk is reidy 

 for drying and luftering; previous to the defcription of which, the author makes feveral re- 

 marks to the following purport : 



Though the mineral acids are the moft powerful and deftruflive of all faline fubftances, 

 yet they may be applied to filk when diluted with fpiiit of wine in very confidcrable dofes. 

 In trials made to afccrtain the maximum, two ounces of marine acid were added to one 

 pound of fpirit of wine, without altering the filk. Two drams of marine acid caufe a very 

 perceptible alteration in one pound of filk. I fuppofc he means pure acid, or perhaps di- 

 luted with water ; for the paflage as it ftands is obfcurc. Numerous experiments have 



F 2 (hewn 



