| XXX | (564) | XXX |
5 ^4
B
L
E
A
C
BUCKING and BOILING. This is the mod important operation of the whole procefs, and deferves a thorough examinatio'n. Its defign is to Idofen, and carry off, by the help of alkaline lixives or lyes, that particular fubftance in cloth, which is the caufe of its brown colour. All afhes ufed in lye, the pearl excepted, ought to be wed pounded, before they are put into the copper; for the Marcoft and Calhub are very hard, and with fome difficulty yield their fails. As thefe two laft contain a very confiderable proportion of a real fulphureous matter, Which mud in fome degree tinge white cloth ; and as this is diflblved much more by boiling, than by the inferior degrees of heat, while the falts may be as well extradied by the latter. The water ffiould never be brought to boil, and fhould be continued for fome time longer under that degree of heat. The pearl-affies diould never be put in till near the end, as they are eafily diffolved in water. If the falts were always of an equal drength, the fame quantities would make a lye equally drong; but they are not. Salts of the fame name'differ very much from one another. The Mufcovy alhes are turning weaker every day, gs every bleacher mud have obferved, till at lad they turn quite feffetei A decodion from them when new, mud differ very much from one when th|ey have been long kept. Hence a neceffity of fome exadt criterion to difcover when lyes are of an equal drength. The tade cannot ferve, as that is fo variable, cannot be defcribed to another, and is blunted by repeated trials. The proof-ball will ferve the purpofe of the bleachfield fufficiently ; and, by difcovering the fpecific gravity, will fhow the quantity of alkaline falts diffolved. But it cannot fhow the dangerous qualities of thefe falts; for the lefs caudic and lefs heavy this liquor is, the more dangerous and corrofive it rmfy be for the cloth. The third lye, which they draw from thefe materials by an infufion of cold water, in which the tade of lime is dil’coverable, appears plainly to be more dangerous than the fird. The fecond lye, which they extradl from the fame affies, and which is reckoned about a third in drength, when compared to the fird, mud be of the fame nature ; nor fhould it be ufed without an addition of pearl-afhes, which will correid. it. It is taken for a general rule, That the folution of any body in its mendmum is equally diffufed through the whole liquor. The bleachers depending on this, ufe equal quantities of the top and bottom of their lye, when once clear and fettled; taking it for granted, that there is an equal quantity of falts in equal quantities of the lye. But if there is not, the midake may be of fatal confequence, as the lye may be.in fome places dronger than what the cloth can'with fafety bear. That general law of folution mud have taken its rife from particular experiments, and not from reafoning. Whether a fufficient number of experiments have been tried'to afcertain this point, and to edablifh an undoubted general rule, may be called in quedion. “ But, fays Dr Home, .when I had difcovered that
KING. lime makes part of the diffolved fubdance, and relieved how long its groffer parts will continue fufpended in water, there appeared dronger reafons for Cufpefting that this rule, though it may be pretty general, does not ake place here ; at leaf! it is worth the purfuit of experiment. “ I weighed at the bleachfield apiece of glafs in fome cold lye, after it had been boiled, dood for two days, and about the fourth part of it had been ufed. The glafs weighed 3 drachms 14 grains in the lye, and 3 rVachms y-y grains in river-water. The fame glafs weighed in the fame lye, when almod all ufed, 2 grains lefs than it had done, before. This ffiows, that the lad of the lye contained a third more of the diffolved body; and, confequently, was a third dronger than the fird of the lye. “ As this might, perhaps, be owing to a continhation of the folution of the falts, I repeated the experiment in a different way. “ I took from the furface fome of the lye, after the falts were diffolved, and the liquor was become clear. At the fame time I immerfed a bottle, fixed to a Jong dick, fo near the bottom, as not to raife the afhes there, and, by pulling out the cork by a firing, filled the bottle full of the lye near the bottom. The glafs weighed in river-water 3 drachms 384 grains; in the lye taken irom the furface 3^ drachms 34-r grains; and in the lye taken from the bottom 3 drachms 314 grains. This experiment fhows, that the lye at tty: bottom was, in this cafe, 4 dronger then the lye at the furface, “ At other times when I tried the fame experiment, I found no difference in .the fpecific gravity; and therefore, I leave it as a quedion yet doubtful, though deferring to be afcertained by thofe who have an opportunity of doing it. As the lye ftands continually on the afhes, there can be no doubt but what is ufed lad mud be dronger than the fird. I would, therefore, recommend, to general praflice, the method ufed by Mr John Chriflie, who draws off the lye, af|er it has fettled, into a fecond receptacle, and leaves the afhes behind. By this means it never can turn dronger; and he has it in his power to mix the 'top and bottojn, which cannot be done fo long as it dands on the affies.” Having confidered the lye, let us next inquire how it, afts. On this inquiry depends almod the whole theory of bleaching, as its adion on cloth is, at lead in this country, abfolutely neceffary. It is found by experiment, that one effed they have on cloth, is the diminiffiing of its weight; and that their whitening power is, generally, in proportion to their Weakening power. Hence arifes a probability, that thefe lyes ad by removing fomewhat from the cloth, and that the lofs of this fubffahce is the caufe of uhitenefs. This appears yet plainer, when the bucking, which lads from Saturday night to Monday morning is attended to. There are various and different opinions with regard to the operation of thefe falts: That they ad by altering the external texture of the cloth, or by feparating the mucilaginous parts from the' red, or b,y extrading the oil which is laid up in the cells of the plant The lad is the general opinion, or rather conjedure, for none of them deferves any better name ; but may we venture to affirm, that it is fo without any better ti;le to pre-eminence.
