| XXX | (566) | XXX |
5<j<$ BLEACHING. vegetables are immediately put into boiling water by experiment, helps to confirm this ; for it feemedto whiten cooks, that thefe fubftances may preferve their green co- moft when the laft panicles of water were going off. lour, which is only to be done by hindering them from This continual evaporation from the furface of the turning too foft. Boiling water has the fame effeft on cloth /hows, that the deiign of the operation is to carry animal fubflances; for if fait beef is put into it, the wa- off fomewhat remaining after the former procefs of buckter is kept from getting at the falls, from the outfide of ing. This appears likewife from a fact known to all bleachers, that the upper fide of cloth, where the evathe beef being hardened. But when we confider, how much of an oily fubftance poration is ftrongeft, attains to a greater degree of whitethere is in the cloth, efpecially at firft, which will for nefs than the under fide. But it is placed beyond all fome time keep off the water, and how the twilling of doubt by experiment, which /hews, that cloth turns much the threads, and clofenefs of the texture, hinders the lighter by being expofed to the influence of the fun, air, water from penetrating, we lhall find, that if boiling wa- and winds, even though the falts have been wa/hed out ter were put on it at once, the cloth might be liable, in of it. feveral parts, to a dry heat, which would be much worfe What, then, is this fubftance ? As we have difeovered than a wet one. That the lyes have not accefs to all in the former fedlion, that the whitening, in the operaparts of the cloth, at firft, appears plainly from this, tion of bucking, depends on the extradhng or loofening that when it has lain, after the firft bucking, till all the the heavy oil, and folid particles of the flax ; it appears lyes are wailted out, it is as black, in fome parts, as highly probable, that the effefts of watering, and expowhen it was fteeped. This muft be owing to the dif- fition to the fun, air, and winds, are produced by the cbarge of the, colouring particles, from thofe places to evaporation of the fame fubftance, joined to the falts, which the lye has accefs, 'and to their remaining where with which compofite body the cloth is impregnated when it has not. It would feem advifeable, then, in the firft expofed on the-field. That thefe falts are in a great bucking or two, when the cloth is foul, to ufe the lye meafure carried off or deftrpyed, appears from the cloth’s confiderably below the boiling point; that by this foak- being allowed to dry without any danger, after the evaing or maceration, the foulnefs may be entirely difcharg- poration has gone on for fome time. “ If we can /how, ed, and the cloth quite opened for the fpeedy reception fays Dr Home, that oils and falts, when joined together, are capable of being exhaled, in this manner, by of the boiling lye in the buckings which follow. The lyes firould likewife be weakeft in the firft buck- the heat of the atmofphere, we /hall reduce this queftion ings, becaufe then they a<ft only on the more external to a very great degree of certainty. parts ; whereas, when the cloth is more opened, and “ Sept. to. I expofed, in a fouth-weft window, half the field of addon is increafed, the adtive powers ought an oz. of Caftile foap, fliced down, and watered. Sept. to be fo too. For this reafon they are at the ftrongeft 14. when well dried, it weighed but 3 dr. 6 gr. Sept. after fome fourings. 22. it weighed 2 dr. 2 gr. Sept. 24. it weighed 1 dr.. The only thing that now remains to be confidered, is, 50 gr. It then feemedavery little whiter; but was much the management of the coarfe cloth, where boiling is fub- more mucilaginous in its tafte, and had no degree of faltftituted in place of bucking. This fpecies of linen cannot nefs, which it had before. afford the time and labour neceffary for the latter ope- “ It appears from this experiment, that foap is fo voration ; and therefore they muft undergo a ftiorter, and latile, when watered, and expofed to air not very warm, more active method. As the heat continues longer at that it lofes above the half its weight in fourteen days. the degree of boiling, the lyes ufed to the coarfe cloth The fame muft happen to the faponaceous fubftance, muft be weaker than thofe ufed to the fine. There is formed from the conjunftion of the alkaline falts, heavy not fo much danger from heat in the coarfe as in the fine oil, and earthy particles of the flax. The whole defign, cloth, becaufe the former is of a more open texture, and then, of this operation, which, by way of pre-eminence, will allow the lye to. penetrate more fpeedily. In the gets the name of bleaching, is to carry off, by the evaclofer kinds, however, the firft application of the (alts poration of water, whatever has been loofened by the former procefs of bucking. fliould be made without a boiling heat. “ Againft this do&rine there may be brought two obfeemingly of great weight. It is a general opiALTERNATE WATERING and DRYING. je&ions, nion among/! bleachers, that linen whitens quicker in After the cloth has been bucked, it is carried out to March and April, than in any other months : But as the the field, and frequently watered for the firft fix hours. evaporation cannot be fo great at that time, as when the For if during that time, when it is ftrongly impregnated fun has a greater heat; hence the whitening of cloth is with falts, it is allowed to dry, the falts approaching not in proportion to the degree of evaporation; and clofer together, and, aflifted by a greater degree of heat, therefore the former cannot be owing to the latter. This increafing always in proportion to the drinefs of the cloth, obje&ion vani/hes, when we confider, that the cloth aA with greater force, and deftroy its very texture. Af- which comes firft into the bleachfield, in the fpring, is ter this time, dry fpots are allowed to appear before clofely attended, having no other to interfere with it for it gets 3ny water. In this ftate it profits moft, as the fome time ; and, as it is the whittft, gets, in the after bucklatter part of the evaporation comes from the more ma- ings, the firft of the lye; while the fecond parcel is’often, ternal parts of the cloth, and will carry away moft: from bucked with what has been ufed to the firft. Were the thofe parts. The bleaching of the wax, in a preceding fa<ft true, on which the objedion is founded, this would
