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manner as the common black pigments settle from diluted gumwater. The ink, kept moist, in warm weather, becomes in a few days putrid, like the Auid or soft parts of animals; as does likewise the clear water, after the black matter has settled and separated from it. The Indian-ink appears therefore to contain an animal substance soluble in water; and to consist of a black powder mixed with some animal glue. For the greater certainty, in regard to this conglutinating ingredient, I boiled one of the China cakes in several frefh portions of water, that all its foJuble parts might be extracted, and having filtered the liquors through paper, set them to evaporate in a stone bason: they Imelt like glue, and left a very considerable quantity of a tenacious substance, which could not be perceived to differ in any respe&t from common glue.
Being thus convinced of the compofition of the mass, I tried to imitate it, by mixing some 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, answered fuliy 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 small pains, had the same effect with the lamp-black; but in the state in which ivory-black is commonly sold, it proved much too gritty, and separated too hasily from the water.'
The conclusions from these experiments we find confirmed by Du Halde, in his History 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 missionaries. The colouriny-matter in all these receipts is lamp-black, and in one of them there is added a quantity of horse-chesnut, burnt till the smoke ceases : the conglutinating ingredient, in one, is a thin size of neats leather ; in another, a solution of gacanth; and in the third, a inixture of size with a decoction of certain vegetables to us unknown.- In the appendix to this vol. Dr. Lewis observes, that the gum tragacanth, here mentioned, is not the conglutinating matter in any of the samples of Indian-ink which he has examined; that the vegetable decoctians can be of no use where fize is employed, unle's to scent the composition ; and that the receipt, of lamp-black and a thin fize of neats leather, is the very composition pointed out by bis experiments.
Of Compositions for marking Sheep. Great quantities of wool are annually made unserviceable by the pitch and tar, with which the farmer marks his Sheep : these, as they considerably increase the weight of the fleece at
a trifing expence, are not laid on with a sparing 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 set of experiments in order to discover an innocent composition for this purpose: the requisite qualities of such a composition are, that it be cheap, and that the colour be strong and lasting, so 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 soap or size; resins, likewise oils or fats, may be joined with the colouring matters for this use, and may by the same additions be corected. On these principles many trials were made, but with little success ; for the unctuous and refinous materials, with the advantage which they received from soap or size, of being easily washed out from the woul, received also the disadvantage of being soon washed out by the weather.
• It was next considered, fays Dr. Lewis, that as wool has always a natural greasiness, which the workmen wash out with Itale urine, soap, or ley, as described in the sequel of this hiftory, the common animal fats might probably be discharged from it by the fame means, so as not to stand in need of those ingredients, from which the foregoing compositions had contracted the imperfection of being too easily dischargeable. Accordingly I melted some tallow; and stirred into it so much charcoal, in fine powder, as made it of a full black colour, and of a thick consistence. This mixture, easily procurable and at small expence, being applied warm with a marking iron on pieces of Aannel, quickly fixed or hardened, bore moderate Jubbing, resisted the sun and rain, and yet could be washed out freely with soap, or ley, or ftale urine.
'Though the mixture of tallow and charcoal-powder was found suficiently durable when applied as above upon pieces of flannel, it occurred, that nevertheless, it might, by the repeated attritions to which it is exposed on the body of the animal, be in danger of being rubbed off too soon. If we could add to the composition a little piich or tar, we should effectually secure against any inconveniency of this kind, and it was apprehended that these ingredients might here be added with safety; for being perfectly diffolved by the talow, it might be presumed that they would wath 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 discharged by the same detergents that oil itself would be. I therefore melted soine tallow, with an eighth, with a sixth, and with a fourth of ies weight of tar, and having thickened the mixtures with charcoalpowder, fpread them while hot upon pieces of flannel. None of the compositions could be discharged by any rubbing or washing with water. By soap they were all washed out completely; that which had the smallest 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 desired of this quality may be communicated, without damaging the wool, by a proper addition of the substances commonly made use of.'
Of Compositions for preserving Wood, &c. The best preparation for coating or painting wood does not, in all cases, contribute to its preservation ; for if the wood be not thoroughly dry, especially those kinds of wood, the juices of which are not oily or refinous, the coating confines the watery fap, and hastens the corruption : but where the wood is properly dried, these compofitions have their use.—Pitch and tar make the basis of these compositions; 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 sun. Different powders, ashes, ochres, and other mineral pigments, have been tried, but without apswering the purpose so well as could be wished. Two compositions likewise, recommended in the Swedish Transactions, were examined by our Author; but he gives the preference to the following composition : the finest coloured pieces of pitcoal are to be ground to an impalpable powder, and to be added to the melted tar in such a proportion, as to be freely spread with the brush
while warm.--The following curious anecdote is related by Dr. Lewis.
• 'l he mixture of tar and lamp-black is found the most effectual preservative for the masts and yards of ships. Such parts of the mast, as the sliding up and down of the fails requires to be only greased, and those which are covered with turpentine or resin 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 vessel in the East-Indies, with an account of a violent thunder-storm, by which the mainmast was greatly damaged, and the effects of which on the different parts of the mast were pretty remarkable. All the parts which were greased, or covered with turpentine, were burst in pieces : those above, between, and below the greased parts, as also the yard-arms, the round-top, or scaffold. ing, &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 solution of gum-arabic or size, forin the papier maché. From this are made a great variety of toys, &c. by pressing it while moist into oiled moulds. A black varnith, hard, durable, and glossy, 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 vefsel, and thrice as much amber in fine powder sprinkled in by degrees, with the addition of a little spirit or oil of turpentine now and then : when the amber is melted, sprinkle in the same quantity of sarcocolla, continuing to stir them, and to add more spirit of turpentine, till the whole becomes fluid: then strain out the clear through a coarse hair bag, prefling 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 set 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 simple amber-varnish is prepared, by gently melting the amber in a crucible till it becomes black, and then boiling and diffolving this black fubstance, first reduced to a powder, in linseed-oil, or in a mixture of linseed oil and oil of turpentine.
By melting the amber in this process, it suffers a decompofition, its nature is changed, and part of its oily and saline matter expelled. The same changes occur in the common diftillation of this subject : and when the distillation is not pushed too far, the shining black mass which remains after the thinner oil and greater part of the salt have arisen, is in such a proportion soluble in oils, as to supply the common demand of the varnihmakers. This decomposition however is not neceffary, as has generally been supposed, in order to the solution : from the curious experiments of Hoffman, Stockar, Zeigler and others, it appears, that amber may be perfectly diffolved, in expressed oils, in turpentine, and in balsam of copaiba ; if it be exposed to the action of these menstrua in close stopt vessels, and afGfted by a due degree of heat.-The solution may be more expeditiously made, if the fire be so strong as to convert part of the oil into elastic vapours ; care must be taken to give such a vent to these vapours, as not to endanger the bursting of the vessel.
The folution, says Ďr. Lewis, in rapeseed-oil, and in oil of almonds, was of a fine yellowish colour; in linseed-oil, goldcoloured ; in oil of poppy-seeds, 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 last oil, which
Ds. Lewis met with the first account of this varnish, in a pamphlet on Drawing, &c. printed for Mr. Peele in 1732, and said to be taken chiefly from manuscripts left by Mr. Boyle,
of itself, in the greatest common heat of the atmosphere, proves of a thick butyraceous confiftence, continued fluid when the amber was diffolved in it. The solutions made with turpentine, and with balsam of copaiba, were of a deep red colour, and on cooling hardened into a brittle mass of the fame colour. All the solutions 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 bard, tenacious, glossy varnishes, which dried sufficiently quick, and appeared greatly preferable to those made in the common man. ner, from melted amber.'
Of Sealing-wax. * Black sealing-wax is composed 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 shell-lac, answers as well for this use as the finest. It is customary to mix with it, for the ordinary kinds of sealing-wax, a considerable proportion, as twothirds its weight, of the cheaper resinous bodies, particularly Venice purpentine, by which the beauty of the mass is here less injured than in the red wax, and of which a small addition is in all cases 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 soft, into sticks, which afterwards receive their glossiness by being heated till the surface begins to shine.
The black figures on the dial-plates of clocks and watches, which look like black enamel, are formed of the finer kind of black sealing-wax, which is melted into cavities made in the plate, and afterwards polished. Black enamel, or ftones, are sometimes imitated in the same manner in other works.
Of Printing-ink. The usual composition for printing-ink consists of lamp-black and expressed oil. The oil, previous to its being united with the lamp-black, passes through a particular process, and suffers a considerable alteration.- By the proper application of fire, its consistence and tenacity are increased; its greafiness and unic.
More properly called Stick-lac.- -Lac is a concrete britile fubAance, said to be collected from certain trees by a winged red insea, and deposited 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 insects, it is of an intermediate nature between wax and resios