freed from the fixed air, with which in the ufual experiments of chemistry it appears to have a greater affinity than with oil; for foap may be partially decompofed by fixed air, nor can it be prepared without an exceedingly cauftic alkaline ley.

(93.) In this light the matter has appeared to fome very eminent chemifts; and Dr BLACK thought it of importance futficient to publish printed directions to the practical bleachers how to render their alkali fufficiently cauftic with lime, and at the fame time recover it from the chalky refiduum with as little iofs as poffible. This me. thod has accordingly been tried; but does not altogether anfwer the fanguine expectations at first raifed by the propofal. In the large way of operating, fixed alkali quits the fixed air to unite with the oily or other matter to be extracted from the cloth. The only advantage therefore to be gained by Dr Black's improvement is, that the action of the alkali is thus quickened, and fome quantity of fuel faved; but this is not, by the bleachers, reckoned an equivalent to the trouble of render ing the alkali cauftic, unlefs in places where fuel is very fcarce.

PART. II.

publifhed in Edinburgh, we have collected the following particulars.

SECT. I. ACCOUNT of M. BERTHOLLET'S
METHOD of BLEACHING.

(96.) I. M. BERTHOLLET having procured the dephlogisticated marine acid, in as ftrong and concentrated a ftate as he could, immerfed into it thread and cloth; which by that means were confiderably whitened. In a fhort time the liquor feemed to lofe its ftrength; upon which it was poured off, and more put in its place; and so on until the fubftance immerfed became perfectly white. Thus, however, the process was not only very expensive, but the stuff was confiderably injured; fometimes even lofing its cohetion altogether, fo that there was a neceflity for trying fome other method.

(97.) II. Uting a diluted spirit, he fucceeded perfectly in rendering the cloths completely white; but by keeping them for fome time, or expofing them for a little to the action of an alkaline ley, they became again brown or yellow.

(98.) III. On confidering the process of bleaching in the common method, he found that the action of the fun and air are fubfervient to bleaching only as they prepare the colouring particles for being diffolved and separated by alkaline lixi

INTRODUCTION.

(94.) THE ufe of ACIDS, in bleaching, was formerly in a great measure unaccounted for; but from the late difcoveries concerning the ufe of dephlogifticated spirit of falt in this art, it appears probable that they act by means of the dephlogifticated air they contain. This, however, is not always the cafe; for filk is rendered yellow by the action of dephlogifticated air, though rendered white by the action of the volatile fulphureous a cid, which undoubtedly contains a portion of this kind of air, though much less than the concentrated vitriolic acid. The nitrous acid, which contains a great quantity of dephlogifticated air, Jikewife communicates a yellow colour to filk; and indeed feems very much inclined to produce this colour upon all the substances it touches. At any rate, its price would be a fufficient objection against its ufe in' bleaching.

(95.) The marine acid, more generally known by the name of spirit of falt, in its common ftate, is faid by M. Berthollet to be used with fuccefs by fome bleachers in France, in^ead of the vitriolic; but fuch experiments as have been made upon it in this country have net anfwered the purpose. The new method of bleaching is founded upon the remarkable property, which that acid when dephlogisticated poffeffes, of deftroying vegetable colours; and various attempts have been made to introduce it into practice, though in this country the difficulties or difadvantages attending it have prevented it from coming into general ufe, fo that many of our bleachers obftinately perfevere in the old method. M. Scheele was the inventor of this kid of acid; but M. Berthollet seems to have the first who attempted to apply it in the oof bleaching. From a treatife on the hod of bleaching, which has been lately

1

nature of the dews, both fuch as are precipitated from the atmosphere and thofe which tranfpire from vegetables. Both these were found fo ftrongly impregnated with dephlogifticated air, that they deftroyed the colour of paper when faintly tinged with turnfole. Hence he obferves, that it is by no means improbable, that the ancient prejudices concerning May-dews might have arifen from fome obfervations analogous to this; more especially as in that month the transpiration of plants is extremely copious.

(99.) IV. By imitating with the dephlogisticated marine acid and alkaline ley the common procefs of bleaching, he fucceeded in making a perfect and permanent white. For this purpose an alkaline lixivium was employed alternately with the dephlogifticated marine acid; the latter being no longer ufed in a concentrated state. Thus he avoided both the inconvenience arising from the fuffocating fmell of the liquid, and that of its deftroying the texture of the ftuff immersed in it.

(100.) V. The cloth is prepared for bleaching in this manner; by fteeping it 24 hours in water, to extract the dreifing it receives from the weaver : a little old ley, which has already loft the greatest part of its frength in other processes, may be ufed with advantage. It is next to be expofed once or twice to the action of fome good fresh alhaline ley; to feparate, by means of this cheaper liquid, all the colouring matter which it can extract, and thereby fave the dephlogisticated acid.

(101.) VI. The stuff muft next be carefully wathed with water, to feparate any remains of the ley which might adhere to it, and weaken the action of the liquor. It is then to be disposed of in wooden troughs, fo that the dephlogisticated acid may pafs freely through every part of it; to allow which, it muft lie quite loofe, without being tightened or ftraitened in any part.. All thele

troughs

(102.) VII. The firft immerfion in the dephlogifticated acid is to continue 3 hours; after which the cloth is to be removed, and the liquor wrung out of it. It must then be washed a fecond time with alkaline ley; which being alfo washed out, it is to be again immerfed in dephlogisticated acid. (103) VIII. The fecond immersion in the acid is to continue only about half an hour; after which it is to be taken out and wrung as before. The fame liquor may ferve for several immerfions; cly when it appears to be much exhaufted, it is to be reftored by an addition of fresh liquor. (104) IX. After the cloth feems to be fufficiently whitened, excepting only some few black threads and the felvages, it is to be filled with black foap, and frongly rubbed for fome time; after which it is to be again washed in alkaline ley, and receive another immerfion in the acid liquor.

(15.) X. It has not yet been determined what number of immerfions in the acid are neceflary to whiten linen cloth, though our author fuppofes from 6 to 8 to be fufficient for the purpofe. SECT. II. METHOD of PREPARING the DEPHLOGISTICATED MARINE ACID; with a DESCRIPTION of the APPARATUS.

(105) For preparing the dephlogisticated acid, M. Berthollet recommends fix ounces of black manganefe finely powdered, 16 ounces of fea-falt ikewife in powder, and 12 ounces of concentrated vitriolic acid to be diluted with 8 ounces of water: but the quantity of this last must be varied accordng to the Rrength of the acid and the drynefs of the falt. If the manganefe is impure, its quantity is to be augmented in proportion to the fuppofed impurity; and it is known whether a fuflicient quantity has been employed, by a portion remain behind and retaining its black colour. When the materials are prepared, the manganefe and a falt, both reduced to fine powder, muft be mixed accurately together, and put into the durg veifel placed in a fand-bath; the vitriolic a4, dilated with water and allowed to cool, is then to be poured upon tnem, and the junctures exacly luted. The receiver may be of wood cored in the infide with wax, and of a very large ; for the gas is abforbed in proportion to the tface of the water it acts upon.

M. BERTHOLLET deferibes an apparatus, complicated, but of which we have given a reprefentation in Plate XXXIX. Fig. 1. is an evation of the apparatus, in which is reprefented a reverberatory furnace A B CD, having, on ne with B, many fmall openings in its circumference, to ferve as chimneys; within which, upon and-bath a, is placed a matrafs b, the neck of wch ftands out above the furnace, running through the opening D, which is to be clofed th clay. The mouth F, of the neck of the mals, is clofed by a cork G, through the midck of which paffes a tube H, which forms a communication between the infide of the matrafs b, and the intermediate veffel K, where it allo paties Brough a cork 1, which clofes one of the three

(109.) Fig. 2. UPPER PART of the PNEUMATIC

TUB.

In this QRST are four ftaves which are thicker than the others, and which project within the tub, where they are hollowed fo as to receive the ends of two wooden bars U V, which ferve to keep in their places the cavities or receivers X.

(110.) Fig. 3. SECTION of the TUB. Each cavity X is fo conftructed that it may receive the gas which is emitted at i from the tube of communication M. The gas, as it comes out, is collected under the lowest cavity, and increases in quantity until it passes by the funnel Z to that in the middle, and afterwards to the upper one.The opening through which the agitator E paffes, in the centre of each cavity, is in the fhape of a funnel, and is fo formed as to hinder the gas from efcaping along the agitator, which is furnished with three tranfverfe arms, c, c, c, each being fastened by a wedge d, d, d,ef reprefents one of thefe arms in a horizontal direction. The bent tube gb ferves to draw of the atmospheric air which is contained under the cavities, after the tube has been filled with water. To make ufe of this tube, the bent part is fucceffively introduced under each cavity, as is fhewn at g; we must then blow into it, at the end h, till the water in it is forced out after which the air contained under the cavity will immediately make its escape.

(11.) Fig. 4. APPARATUS for the DISTILLA TION of MURIATIC ACID. In this, I represents a retort, which is to be placed in a reverbatory furnace; the mouth of the retort is to be closed by a cork m, having two holes, through one of which paffes the tube n, bent at o, and terminating at the top in the form of a funnel p, by means of which the vitriolic acid is to be introduced into the retort. The other hole of the cork m receives the end of a tube q, which forms a communication between the retort and a veffelr; which veffet has thrée openings, and is to be about part full of water, into which is to be plunged the tube of jafety s, to prevent danger from regurgitation: the veffelr has a communication with a fecond veffel u, by means of the tube : this fecond veffel is to be half full of water, and is to have a

communi.

communication with a 3d fimilar veffel: this 3d veffel fhould be alfo provided with a tube of fafety, and should communicate with a 4th.

(112.) In the construction of an apparatus for this purpose, it is evident the requifites are, that the receiver fhould not only be capacious but broad, that the gas, which is very volatile, may meet with a large furface of water to absorb as much of it as poffible. It is very improbable, however, that all the gas can be absorbed by a fingle receiver, let us make it as large as we will; for which reafon it will be proper to have feveral of them connected with each other by glafs tubes, fo that what escapes from one may be obferved by another. Thus we are fure of having the water fully impregnated with the gas; though we cannot by any means concentrate this liquid like the mineral acids.

(113.) By means of condenfing engines, indeed, a greater quantity of it might be forced into the water than it can naturally contain: but this could anfwer no useful purpose; for the moment that a bottle containing fuch liquor was opened, the fuperfluous gas would fly off, with violence and danger to the perfon who opened it. The bottles themfelves would also be liable to burft on every flight alteration of temperature in the atmosphere. It is proper, therefore, not to attempt the preparation of the liquor, in any great degree of ftrength; though this is indeed attended with a very considerable inconvenience, viz. the difficulty of tranfporting it from the place where it is prepared to the bleachfield, on account of the great bulk and weight of it. M. Berthollet propofes to have it made at the place where the cloth is to be bleached; and fo near that the dephlogisticated spirit of falt might be conveyed by fpouts to the troughs which contain the cloth. This, however, muft in many cafes be impracticable, unless we fuppofe the generality of bleachers to be poffeffed of a fkill in managing chemical operations, which at prefent they have not. When great quantities of liquor are to be brought from diftant places, however, it must undoubtedly be a great difcourage ment, efpecially if the beft methods, and the cheapest also, have not been used in the preparation of the acid.

SECT. III. ADVANTAGES of the NEW METHOD of BLEACHING.

(114.) It would add much to the importance of this new method of bleaching, if a comparative eftimate of the expence of that and of the old mode were fairly laid before the public, and the preference in this refpect appeared juftly due to the former. This, however, has not yet been done; nor even the firft and most effential ftep towards it taken, viz. the determining how much ftuff a certain quantity of dephlogifticated spirit of falt will whiten. From fuch experiments as have been made on the fubject, it is probable, that the acid drawn from one pound of falt will whiten 4 of linen cloth without any addition.— This may feem a finall expence; but if we confider the vitriolic acid to be made ufe of, and that the refiduum is ufelefs, it would foon be found very confiderable. Glauber's falt may indeed be pued from the refiduum of the diftillation;

but fo much of that article is prepared otherwise, that at prefent the making of it is no object. M. Berthollet mentions the feparation of the mineral alkali from the refiduum; and fays he has received fome inftructions on this head from M. Morveau and others, but conceals them on account of their being communicated as fecrets.

(115.) To enable the reader to judge for himself of the expence of M. Berthollet's method, we infert the latter part of his memoir, in which this part of the fubject is more particularly confidered. (116.) “If (fays he) at prefent, when the oxygenated muriatic acid cofts nearly three deniers (about half an English farthing a quart,) in the provinces which are not fubject to the GABELLE, (a tax no longer exifting in France,) the new method of bleaching, when properly conducted, is frequently advantageous notwithstanding this expence; it is not to be doubted but that it may become much more fo, by means of thefe œconomical practices which I have juft mentioned. But, fo long as the preparation of the bleaching liquor is at all expenfive, there will always be a great advantage in favour of fine cloths; because, in equal quantities of furface, they prefent a lefs quantity of matter, and are bleached much eafier; fo that an ell, or a pound, of fine cloth, requires much lefs liquor than an ell, or a pound, of coarfer cloth.

(117.) But, that the advantages of this procefs may be fully enjoyed, it is neceffary to cftablifh it in a country which is not fubject to the tax on falt, called the gabelle; for, where falt is not at a low price, the oxygenated muriatic acid becomes too expenfive.

(118.) "Nevertheless, it is not by the expence of the new procefs, rigorously compared with that of the ordinary method of bleaching, that we muft judge of its advantages, as it is attended with fome particular ones which would compenfate a fuperior price. Cloths and thread, which in fome places require many months, may be eafily bleached in five or fix days, even in a large manufactory; and the bleaching of a few pieces only, may, without difficulty, be terminated in two or three days. Betides, the new method of bleaching may be executed in the winter as well as in the fummer, only the drying requires more

time.

(119.) "An induftrious countryman, whose family employ their intervals of leifure in fpinning, is obliged to wait for favourable weather, and perhaps to fend his thread and cloths to a great diftance, where they remain a long time in bleaching; or, if his neceffities are preffing, he is obliged to fell them, at a lofs, to fome intermediate factor, who lays a tax upon his poverty. But, if the manufactories for making oxygenated muriatic acid increase in number fufficiently, thofe who weave a piece of cloth will be able to bleach it themfelves, and to enjoy the whole fruit of their labour, as foon as it is out of their hands.

(120.) "The warehouseman, in a feafon which is unfavourable to the ordinary method of bleaching, is not able to fulfil his engagements without great difficulty; he is obliged to employ a confiderable capital to fill his warehoufe, in the feafon in which the bleaching is executed; he is un

able