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manner as the common black pigments fettle from diluted gumwater. The ink, kept moift, in warm weather, becomes in a few days putrid, like the fluid or foft parts of animals; as does likewife the clear water, after the black matter has fettled and Separated from it. The Indian-ink appears therefore to contain an animal substance foluble in water; and to confift of a black powder mixed with fome animal glue. For the greater certainty, in regard to this conglutinating ingredient, I boiled one of the China cakes in feveral frefh portions of water, that all its foluble parts might be extracted, and having filtered the liquors through paper, fet them to evaporate in a stone bafon: they fmelt like glue, and left a very confiderable quantity of a tenacious fubftance, which could not be perceived to differ in any refpect from common glue.

Being thus convinced of the compofition of the mass, I tried to imitate it, by mixing fome of the lamp-black, which I had myself prepared from oil, with as much melted glue as gave it fufficient tenacity for being formed into cakes. The cakes, when dry, anfwered fully as well as the genuine Indian-ink, in regard both to the colour, and the freedom and smoothness of working. Ivory black and other charcoal blacks, levigated to a great degree of fineness, which requires no fmall pains, had the fame effect with the lamp-black; but in the state in which ivory-black is commonly fold, it proved much too gritty, and feparated too hatily from the water.'

The conclufions from thefe experiments we find confirmed by Du Halde, in his Hiftory of China. He gives three receipts for the preparation of Indian-ink, two from Chinese books, and the third communicated by a native to one of the miffionaries. The colouring-matter in all these receipts is lamp-black, and in one of them there is added a quantity of horfe-chefnut, burnt till the fmoke ceafes: the conglutinating ingredient, in one, is a thin fize of neats leather; in another, a folution of gum tragacanth; and in the third, a mixture of fize with a decoction of certain vegetables to us unknown.-In the appendix to this vol. Dr. Lewis obferves, that the gum tragacanth, here mentioned, is not the conglutinating matter in any of the famples of Indian-ink which he has examined; that the vegetable decoctions can be of no use where fize is employed, unle's to scent the compofition; and that the receipt, of lamp-black and a thin fize of neats leather, is the very compofition pointed out by his experiments.

Of Compofitions for marking Sheep.

Great quantities of wool are annually made unferviceable by the pitch and tar, with which the farmer marks his sheep: thefe, as they confiderably increase the weight of the fleece at

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a trifling expence, are not laid on with a fparing hand. It is a matter of importance therefore to the woollen manufactory, and was warmly recommended to our Author by the late Dr. Hales, to go through a fet of experiments in order to dilcover an innocent compofition for this purpofe: the requifite qualities of fuch a compofition are, that it be cheap, and that the colour be strong and lafting, fo as to bear the changes of weather, and other injuries for a due length of time, and not to damage the wool.The ill-qualities of pitch and tar may be corrected by mixing with them foap or fize; refins, likewife oils or fats, may be joined with the colouring matters for this ufe, and may by the fame additions be cor ected.-On thefe principles many trials were made, but with little fuccefs; for the unctuous and refinous materials, with the advantage which they received from foap or fize, of being eafily washed out from the wool, received alfo the difadvantage of being foon washed out by the weather.

It was next confidered, fays Dr. Lewis, that as wool has always a natural greafinefs, which the workmen wash out with ftale urine, foap, or ley, as defcribed in the fequel of this hif tory, the common animal fats might probably be discharged from it by the fame means, fo as not to ftand in need of thofe ingredients, from which the foregoing compofitions had contracted the imperfection of being too eafily difchargeable. Accordingly I melted fome tallow; and stirred into it fo much charcoal, in fine powder, as made it of a full black colour, and of a thick confiftence. This mixture, eafily procurable and at fmall expence, being applied warm with a marking iron on pieces of flannel, quickly fixed or hardened, bore moderate rubbing, refifted the fun and rain, and yet could be washed out freely with foap, or ley, or ftale urine.

Though the mixture of tallow and charcoal-powder was found fufficiently durable when applied as above upon pieces of flannel, it occurred, that neverthelefs, it might, by the repeated attritions to which it is expofed on the body of the animal, be in danger of being rubbed off too foon. If we could add to the compofition a little pitch or tar, we fhould effectually fecure against any inconveniency of this kind, and it was apprehended that thefe ingredients might here be added with fafety; for being perfectly diffolved by the talow, it might be prefun ed that they would wash out along with it from the wool. Thus we fee ftains of tar got out from clothes by means of oil, which diffolving the tar, the whole compound is then difcharged by the fame detergents that oil itself would be. I therefore melted fome tallow, with an eighth, with a fixth, and with a fourth of iss weight of tar, and having thickened the mixtures with charcoalpowder, fpread them while hot upon pieces of flannel. None of the compofitions could be difcharged by any rubbing or wash

ing with water. By foap they were all washed out completely; that which had the fmalleft proportion of tar, easily enough; that which had the largest proportion, difficultly. If therefore it should be feared, that the tallow would fail in point of durability or adhesiveness, which, however, I do not apprehend that it will, it is plain, that as much as can be defired of this quality may be communicated, without damaging the wool, by a proper addition of the fubftances commonly made ufe of.'

Of Compofitions for preferving Wood, &c.

The best preparation for coating or painting wood does not, in all cafes, contribute to its prefervation; for if the wood be not thoroughly dry, especially thofe kinds of wood, the juices of which are not oily or refinous, the coating confines the watery fap, and haftens the corruption: but where the wood is properly dried, thefe compofitions have their use.-Pitch and tar make the bafis of these compofitions; and the point to be gained, is to unite with these such a substance as will prevent their melting and running in the heat of the fun. Different powders, afhes, ochres, and other mineral pigments, have been tried, but without apfwering the purpose fo well as could be wifhed. Two compofitions likewife, recommended in the Swedish Tranfactions, were examined by our Author; but he gives the preference to the following compofition: the fineft coloured pieces of pitcoal are to be ground to an impalpable powder, and to be added to the melted tar in fuch a proportion, as to be freely spread with the brush while warm.-The following curious anecdote is related by Dr. Lewis.

The mixture of tar and lamp-black is found the most effectual preservative for the mafts and yards of fhips. Such parts of the maft, as the fliding up and down of the fails requires. to be only greased, and thofe which are covered with turpentine or refin mixed with tallow or oil, generally contract large rents, while the parts coated with tar and lamp-black remain perfectly found. I have been favoured by a gentleman on board a veffel in the Eaft-Indies, with an account of a violent thunder-ftorm, by which the mainmaft was greatly damaged, and the effects of which on the different parts of the maft were pretty remarkable. All the parts which were greafed, or covered with turpentine, were burst in pieces: thofe above, between, and below the greafed parts, as alfo the yard-arms, the round-top, or fcaffolding, &c. coated with tar and lamp-black, remained all unhurt.

Of Amber-varnishes for Papier Maché, &c.

The cuttings of white or brown paper, boiled in water and beaten in a mortar, till they are reduced into a kind of paste and then boiled with a folution of gum-arabic or fize, form the

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papier maché. From this are made a great variety of toys, &c. by preffing it while moift into oiled moulds.-A black varnish, hard, durable, and gloffy, for coating these toys, &c. is thus prepared Some colophony, or turpentine boiled down till it becomes black and friable, is melted in a glazed earthen vessel, and thrice as much amber in fine powder fprinkled in by degrees, with the addition of a little fpirit or oil of turpentine now and then when the amber is melted, fprinkle in the fame quantity of farcocolla, continuing to ftir them, and to add more fpirit of turpentine, till the whole becomes fluid: then ftrain out the clear through a coarfe hair bag, preffing it gently between hot boards. This varnish, mixed with ivory-black in fine powder, is applied, in a hot room, on the dried paper paste ; which is then fet in a gently heated oven, next day in a hotter oven, and the third day in a very hot one, and let stand each time till the oven is grown cold. The paste thus varnished, bears liquors hot or cold.'

A more fimple amber-varnish is prepared, by gently melting the amber in a crucible till it becomes black, and then boiling and diffolving this black fubstance, firft reduced to a powder, in linfeed-oil, or in a mixture of linfeed-oil and oil of turpentine. -By melting the amber in this procefs, it fuffers a decompoAition, its nature is changed, and part of its oily and faline matter expelled. The fame changes occur in the common distillation of this fubject: and when the diftillation is not pushed too far, the fhining black mafs which remains after the thinner oil and greater part of the falt have arifen, is in such a proportion foluble in oils, as to supply the common demand of the varnishmakers. This decompofition however is not neceffary, as has generally been fuppofed, in order to the folution: from the curious experiments of Hoffman, Stockar, Zeigler and others, it appears, that amber may be perfectly diffolved, in expreffed oils, in turpentine, and in balfam of copaiba; if it be exposed to the action of these menftrua in close stopt veffels, and affifted by a due degree of heat.-The folution may be more expeditiously made, if the fire be fo ftrong as to convert part of the oil into elaftic vapours; care must be taken to give fuch a vent to thefe vapours, as not to endanger the bursting of the vessel.

The folution, fays Dr. Lewis, in rapefeed-oil, and in oil of almonds, was of a fine yellowish colour; in linfeed-oil, goldcoloured; in oil of poppy-feeds, yellowish red; in oil-olive, of a beautiful red; in oil of nuts, deeper coloured; and in oil of bays, of a purple red. It is obfervable that this laft oil, which

Dr. Lewis met with the first account of this varnish, in a pamphlet on Drawing, &c. printed for Mr. Peele in 1732, and faid to be taken chiefly from manufcripts left by Mr. Boyle.

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of itfelf, in the greateft common heat of the atmosphere, proves of a thick butyraceous confiftence, continued fluid when the amber was diffolved in it. The folutions made with turpentine, and with balfam of copaiba, were of a deep red colour, and on cooling hardened into a brittle mafs of the fame colour. All the folutions mingled perfectly with spirit of turpentine. Those made with the oils of linfeed, bays, poppy-feeds, and with nuts, and with balsam of copaiba and turpentine, being diluted with four times their quantity of spirit of turpentine, formed hard, tenacious, gloffy varnishes, which dried fufficiently quick, and appeared greatly preferable to those made in the common manner, from melted amber.'

Of Sealing-wax.

Black fealing-wax is compofed of gum lac*, melted with one half or one third of its weight of ivory-black in fine powder. The inferior fort of lac, called fhell-lac, anfwers as well for this use as the finest. It is customary to mix with it, for the ordinary kinds of fealing-wax, a confiderable proportion, as twothirds its weight, of the cheaper refinous bodies, particularly Venice turpentine, by which the beauty of the mass is here lefs injured than in the red wax, and of which a small addition is in all cafes expedient, to prevent the compound from being too brittle. The ingredients being melted and well stirred together over a moderate fire, the mixture is poured upon an oiled stone or iron plate, and rolled while foft, into fticks, which afterwards receive their gloffiness by being heated till the furface begins to fhine.

The black figures on the dial-plates of clocks and watches, which look like black enamel, are formed of the finer kind of black fealing-wax, which is melted into cavities made in the plate, and afterwards polifhed. Black enamel, or ftones, are fometimes imitated in the fame manner in other works.

Of Printing-ink.

The ufual compofition for printing-ink confifts of lamp-black and expreffed oil. The oil, previous to its being united with the lamp-black, paffes through a particular procefs, and fuffers a confiderable alteration.-By the proper application of fire, its confiftence and tenacity are increased; its greafiness and unc

More properly called Stick-lac.-Lac is a concrete brittle fubftance, faid to be collected from certain trees by a winged red infect, and depofited either on the branches of the trees or on flicks fitted in the earth for that purpose. When freed from the tinging matter it receives from the young infects, it is of an intermediate nature between wax and refins.

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