nicety therefore is requifite to manage this part of in fuch a manner, as to diffolve the particular ma gives the harfhnefs, and yet to damage the filk pofiible.

Mr. Macquer reckons it a difficult and complex af municate black to filk; but experience, Dr. Lew abundantly fhewn the contrary; and from his own o and the particulars of a procefs which Mr. Macqu followed in the manufactories of Gours and Gin Icludes, that filk is not more averfe than wool to t the black dye; and that a good black may be dyed c the fame materials, in the fame method, and wit difpatch, as on wool or woollen cloth. This is firmed by the proce's defcribed in the next fection hats black. The method of our hatters, as I ha formed, fays Dr. Lewis, does not differ materially the French, defcribed in the encyclopedie, which is as

An hundred pounds of logwood, twelve pour and fix pounds of galls, are boiled in a proper water, for fix hours; after which, about fix poun gris and ten of green vitriol are added, and the liqu immering, or of a heat a little below boiling. T dozen of hats are immediately put in, each on its kept down by cross bars for about an hour and a are then taken out and aired, and the fame numb put in their room. The two fets of hats are th aired alternately, eight times each; the liquor bei each time with more of the ingredients but in lefs q at first.

This process affords a very good black on woo ftuffs as well as on hats, as we may fee in the fmall both kinds which are fometimes dyed by the ha workmen lay great ftrefs on the verdegris, and affir cannot dye a hat black without it: it were to be the ufe of this ingredient was more common i branches of the black dye; for the hatters dye, and woollen, is reckoned a finer black than what i produced by the woollen or the filk dyer.'-Our a inquiry is into the method

Of dying linen and cotton black.

The black vitriolic dye, though very durable ftances hitherto mentioned, is perifhable on linen and a method of communicating a full and dura thefe fubjects, has long been one of the defiderata dying. Dr. Lewis has made a number of exper

could bring no procefs to fuch a degree of perfection as to produce the defired effect.There is a curious differtation of the Abbé Mazeas on the red printed cottons of the East Indies, in which he defcribes a method practifed by the Indians, of impregnating their cotton with an animal matter in order to its receiving the red colour. This procefs Dr. Lewis endeavoured to imitate; and tried whether the fame, or a fimilar animal impregnation, would difpofe the fubject to retain the black as effectually as the red dye. The black thus dyed, held the colour better, but not to fuch a degree as to be interefting to the workman. This fhew of fuccefs however, in an unfavourable feason, renders the experiment worthy of being tried again in more advantageous circumftances.

Some printed linens and cottons, fays our author, have a durable black ftain, which, as I am informed by an ingenious and skilful artift, is made with madder and a folution of iron. A quantity of iron is put into four ftrong beer; and to promote the diffolution of the metal, the whole is occafionally well stirred, the liquor at times drawn off, the ruft beaten off from the iron, and the liquor poured on again: a length of time is required for making the impregnation perfect, the folution being reckoned unfit for ufe till it has ftood at leaft a twelvemonth, This folution ftains linen yellow, and of different fhades of buff colour, and is the only known material by which thefe colours can be fixed on linen. The cloth, ftained deep with iron liquor, being afterwards boiled with madder, without any other addition, becomes of the dark colour which we fee on printed cottons and linens, which, if not a perfect black, has a very near resemblance to it. It is fubmitted to the confideration of those whom it may concern, whether this fixt colour would not be preferable, on linen thread, to the perishable black with which thread has hitherto been dyed. It is probable, that even a better black might thus be dyed on thread, than that which the printer on linen produces; for in this laft bufinefs, while fome parts of the linen are ftained deep with the iron liquor, in order to their being made black, others are ftained paler, with the fame liquor diluted with water, for making purple; and others defigned to be red, are prepared with a foJution of alum and fugar of lead: all these colours are dyed in one and the fame copper of madder, with a heat a little below boiling a boiling heat would give a dark tawney or blackih hue to the red, and therefore in this procefs muft neceffarily be avoided; but for the fame reafon it would contribute to deepen the black, and therefore ought always to be called in aid where thread, or entire pieces of linen or cotton, are to be dyed of this colour.'

In the eleventh fection we have an account of the manner of ftaining wood, ivory, bone, horn, hair, marble, agate, &c. back.-This part is concluded with the following curious experiment: Pieces of different ftones, marbles, pebbles, flint, &c. were washed over with a faturated folution of copper made in aqua-fortis: when dry they were put into a crucible, and kept for a little time in a fire juft fufficient to make the vefiel almoft red-hot. All of them were ftained, in the parts which had been moiftened by the folution, of a black colour, durable and pretty deep, though it had penetrated only a very little way into the fubftance of the ftones.

When the smooth furface of an agate, or other ftones not diffolvable in aqua-fortis, is moistened with a copper folution; if a small iron nail be fet upright on its head in the middle, the iron abforbs the acid from the copper, and the copper, now feparating from the fluid, fhoots into fine ramifications like the branches of trees or fhrubs, generally of a very elegant appearance. If the nail be then removed, and the corroded iron carefully washed off by dipping the ftone in water, the vegetations may be changed by heat to the fame black colour as the simple folution of copper in the foregoing experiments, fo as greatly to refemble the figures naturally found in certain ftones, as that called the mocho-ftone. The colour is not indeed fixed on the ftone, like that refulting from the folution of copper alone; but a plate of cryftal laid over it in the manner of a doublet, conceals the imperfection. The only difficulty in this operation confifts in the washing, in which great dexterity is requifite, to separate the corroded iron, which would give a rufty ftain, without wafhing off or difordering the fine vegetations of the copper.'

With the twelfth fection, which treats of black glafs and enamel, Dr. Lewis finishes the firft part of his hiftory of colours. The experiments and inquiries, which make up the remainder of this volume, are folely employed upon the Platina, of which indeed we have a very full hiftory, extended to the length of 169 pages. For this, however, we muft refer our Readers to the work itfelf, as the abftracts and quotations already made have fwelled this article to a very confiderable bulk.

The Appendix, which is added to this volume, contains fuch obfervations and improvements, as occurred to our Author, after the former parts of the work were printed.-Dr. Lewis, when giving an account of the effects of the mineral alcali on platina, refers to the appendix, where he directs a procefs for obtaining this alkali from fea-falt.-Pure fea-falt is compofed of the mineral alkali and the marine acid; if you detach this marine acid by the addition of acid of nitre, or, as it is commonly called, fpirit of nitre, you then obtain cubic nitre, which is a neutral falt formed by the union of the acid of nitre with the mineral

alkali;

alkali and from this compound the mineral alkali is eafily procured in a separate ftate, by deflagration. In order that this process may fucceed, it is neceffary that the fea-falt be pure, confifting only of its acid and the proper alkaline bafis. The general admixtures with fea-falt Dr. Lewis enumerates, and the methods of getting clear from thefe. He then gives directions for obtaining the cubic nitre.

Mr. Marggraff, fays he, in a differtation on the best method of feparating the alkaline fubftance of common falt, found that two parts of smoking spirit of nitre, of such strength as inftantly to fire pure oil of cloves, were fufficient for one part of purified common falt; but of the weaker nitrous fpirit, called aquafortis, he recommends eight times the weight of the falt. He fays the cryftals obtained with the smoking spirit (for he does not seem to have tried the weaker one) were pure cubic nitre, which deflagrated on a burning coal without crackling, and had not the leaft mixture of common falt. Some have reported, that though a pretty ftrong fpirit of nitre was ufed in more than double the weight of the fait, the refiduum after the diftillation confifted chiefly of marine falt unchanged, with only a fmall pro.. portion of cubic nitre intermixed *. On what caufe the failure depended, the few experiments I have made on this head do not enable me to judge: perhaps it may be neceffary that the nitrous fpirit fhould be very ftrong, for a concenterated acid may produce decompofitions, as well as diffolutions, which the fame acid, diluted, is incapable of effecting.'

< The marine alkali being, by the above methods, combined with the nitrous acid, the acid is to be feparated from it by deflagration with inflammable fubftances. Mix the cubic nitre with one fifth, or one fixth of its weight of powdered charcoal, grinding them thoroughly together: the coal of animal fubftances is preferable to that of vegetables, as the latter will leave, after burning, fome fmall portion of an alkaline falt, of a different nature from that which is here required. Throw the mixture, by a very little at a time, into a large crucible made just

The caufe of the failure here mentioned by Dr. Lewis we apprehend to be this; in the distillation of the acid of fea-falt by means of the addition of the acid of nitre, this last is fo volatile as to come over in a confiderable proportion into the receiver, together with the acid of fea falt which it had detached: and the quantity of cubic nitre which is produced muft neceffarily be only in proportion to the quantity of acid of nitre which remains in the retort, and is united with the alkaline falt. To remedy this inconvenience, nothing more is requifite, than frequently to repeat the diftillation with the addition of fresh acid of nitre. Thus the fea-falt will be effectually decompofed, the alkali will be perfectly faturated with the acid of nitre, and nothing will remain in the retort but a pure cubic nitre.

U 4

red-hot,

red-hot, covering the crucible, as fpeedily and as clofe as may be, after each injection, to prevent the matter from being diffipated by the strong deflagration which enfues. When the mixture has been all thrown in, and the detonation has ceased, the fire may be augmented, and a pretty strong red heat kept up for half an hour or more, the crucible during this time being left uncovered. The nitrous acid being thus burnt out, there remains in the crucible a bluish-greenish alkaline mafs, which is to be purified by folution in diftilled water. It diffolves more difficultly than the vegetable alkalies, and, on duly evaporating the folution, fhoots into fine white cryftals, which do not liquify in the air.'

The original of this procefs was firft given by Mr. Boyle; was adopted by the fucceeding chemifts; and is here fully and accurately delivered by Dr. Lewis.-There is a method likewife of obtaining this mineral alkali from another of the native neutral falts. If Glauber's falt, which is a compound of the vitriolic acid and the mineral alkali, be fufed with some powdered charcoal, the vitriolic acid unites with the inflammable principle of the charcoal, and forms common fulphur, at the fame time the alkali is joined with this fulphur and produces an hepar fulphuris; from this again the alkali may be difengaged by means of an acid; if we add the nitrous acid, a cubic nitre is produced, which may be treated according to the foregoing process: if a vegetable acid be employed, the alkali of the hepar fulphuris forms with this a neutral falt, called the polychreftum rupellenfe: in this falt the union of the acid and alkali is fo weak, that it may be eafily diffolved by the action of the fire; a proper calcination therefore diffipates the acid, and leaves the alcali in its pure state.

Dr. Lewis has thus brought to a conclufion the first volume of his Philofophical Commerce of Arts, in which he has been very full upon the following heads: I. The defcription of a portable furnace for making experiments. II. The hiftory of gold, and the various arts and bufineffes depending thereon, III. Experiments of the converfion of glafs veffels into porcelain, and for eftablishing the principles of the art. IV. Of the expansion or contraction of certain bodies at the time of their paffing from a fluid to a folid ftate. V. Of the blowing air into furnaces by a fall of water. VI. The hiftory of colours; Part I. of black colours. VII. The hiftory of platina.

We are forry to obferve, from a paffage in our Author's preface, that the further profecution of this valuable work may now probably be dropt. How far, fays he, thefe principles and thefe views have a juft foundation, or may tend to the advancement of arts and ufeful knowledge, and whether this laborious

and