212. Dr Bancroft mentions, that an acetate of alumine may be prepared more cheaply, by dissolving white lead, not adulterated by carbonate of lime, in strong vinegar, and then adding to the solution a proper proportion of alum. He found also, that litharge, dissolved in vine gar, instead of white lead, was equally useful for de composing alum. The pyroligneous acid, as it was for merly termed, may be substituted very advantageously for vinegar, to dissolve the oxide or carbonate of lead ; and the acetate of lead thus formed, united with the empyreumatic oil which comes over along with the acid, may be employed instead of the common acetate of lead, for decomposing alum. It has also been recently dis covered, that lime, dissolved in the pyroligneous, or other acetic acid, may be employed with still greater advantage for decomposing alum, and forming the ace tate of alurnine. See Philosophy of Permanent Colours, vol. i. p. 366.
213. The solution of tin usually employed by the dyers, and which they term spirit, is prepared with a very dilute nitric acid, called in the language of the shops, Single Aquafortis. In this state, nitric acid is capable, at its ordinary degree of concentration, to dis solve about one-eighth of its weight of tin previously reduced to a granulated form, by pouring it, when melt ed, into water briskly agitated with a bundle of small rods. From one to two ounces of sea salt are commonly added for each pound of acid, though some prefer the muriate of ammonia (sal ammoniac). The acid is diluted with half its bulk of water, to moderate the energy of its action with the tin : a circumstance which seems to be of the utmost importance to the proper preparation of the mordant. The solutions of tin which are made most slowly, and with the least decomposition of the acid, have been found to answer the purpose best ; pro bably. as Dr Bancroft observes, because the tin is less calcined, or oxygenated, and the solution is thus enabled to retain a larger proportion of nitrogen. Two ounces of granulated tin are usually allotted to every pound of aquafortis; the tin being added in minute portions, and at separate intervals, to prevent the solution proceeding too rapidly. The quantity of water which is employed to dilute the acid should he carefully noted down, in or der that a suitable allowance may be made for deteimin ing the proportion of the metallic oxide contained in a given quantity of the solution, which is generally one fourteenth part of the whole, 214. Other preparations of tin have been proposed and employed as mordants. Hellot took eight ounces of nitric acid mixed with an equal quantity of water, and dissolved in it gradually half an ounce of very white sal ammoniac, two drachms of pure nitre, and afterwards half an ounce of granulated tin. Schafer dissolved one part of tin in four parts of nitro-muriatic acid. Mac quer dissolved three parts of tin in eight parts of nitric acid, with which he mixed one part of sal ammoniac and six parts of water. Pcerner put an ounce and a half of sal ammoniac into a pound of nitric acid mixed with a pound of water, and in the liquor he dissolved two oun ces of tin. Guliliche mixed a pound of fuming nitrous
acid with a pound of water, and two ounces of sal am moniac, and this liquor he saturated with as much tin as it could dissolve, adding it by small quantities at a time. After many trials, Berthollet found, that the so lution which gave the most beautiful colour with cochi neal, both in wool and silk, and which could also be pre served the longest without being changed into a gelatin ous precipitate, was prepared by dissolving in nitric acid of the specific gravity 1.24, (water being I,) one, eighth of its weight of muriate of ammonia, adding by small portions an eighth of its weight of tin, and after wards diluting the solution with a fourth of its weight of water.
215. Dr Bancroft has examined, with great care, and at no small expence, the different salts of tin, and the effects which they produce as mordants. We shall use the liberty of giving an abstract of the results of his ex periments. Cochineal, with a solution of tin by muria tic acid, only dyed a beautiful crimson or rose colour ; and with a solution of that metal by a mixture of tartar and muriatic acid, a beautiful scarlet. The same colour ing matter produced, with tin dissolved by a mixture of muriatic and pyroligneous acid, a dark crimson. Cochi neal, with tin calcined by the long continued action of sulphuric acid, dyed a salmon colour; and with a recent solution of tin, it produced a reddish salmon colour, in clining a little to crimson. Tin dissolved by the pure acid of tartar, dyed with cochineal, on cloth, a very lively and beautiful scarlet, inclining a little to orange. A similar colour was produced by water saturated with cream of tartar, in which granulated tin had been kept six weeks. Tin may be readily dissolved by pure citric acid, and more slowly by lemon juice. The solution, freshly prepared, dyes with cochineal a very beautiful scarlet. If it were not too costly, says Dr Bancroft, this solution would deserve the preference of every other for dyeing that colour Tin dissolved by the pyroligneous acid, produced with cochineal a colour between scarlet and a rose colour. Phosphoric acid produced a perma nently transparent and colourless solution of tin, which, with cochineal, dyed a bright yellowish scarlet. Tin dissolved by fluuric acid, produced with cochineal a very bright scarlet. Tin dissolved by a direct mixture of pure nitric and muriatic acids, in equal proportions, the former of the specific gravity of 1.5, and the latter of 1 17, produced with cochineal, and the common allow ance of tartar, a very bright lively scarlet. A similar solution, with an addition of sulphuric acid equal to one fourth of the nitric, yielded only a salmon colour; the oxide of tin having been precipitated from the common dyers' spirit by soda, and afterwards dissolved by sul phuile acid, was as incapable of dyeing, with cochineal, any colour more elevated than twange.