BLOOD, last line of no 27. for brimstone read limestone.
Mr Brown has made a number of experiments on solutions of the different metals precipitated by alkalis impregnated with the phlogiston of blood, as in the making of Prussian blue. This lixivium being poured into a solution of silver in aqua fortis, produces a coagulum of a pure flesh-colour. The like lixivium made with flesh instead of blood, produces, in this case, a white coagulum; and simple oil of tartar being used in the same experiment, by way of comparison with these lixivia, afforded a much whiter sediment. Spirit of salt being added severally to all the three mixtures, the bloom of the flesh-colour was taken off in the first; but it suffered no other change. In the second, the coagulum was tinged a little blue; and in the third, the whiteness was evidently improved. The bluish tinge in the second case is not wholly to be attributed to the flesh; but perhaps might be owing to an alloy of copper in the silver, from which it is seldom entirely freed.
The same liquors were made use of to form a precipitate from corrosive sublimate of mercury dissolved in water: the consequence of which was, that the lixivium with the blood produced a pure yellow; that with flesh, an orange colour; and the simple oil of tartar, a dingy red. The addition of spirit of salt afterwards to these made some very odd alterations; for the first changed its yellow into an orange colour, and the second its orange colour to a blue, while the third became without any colour. The blue colour in the lixivium with the flesh, when mixed with this solution, may be accounted for from the vitriol in this preparation; but it is not so easy to say, why the same vitriol should not have produced also a blue in a lixivium with blood.
Copper, when dissolved in aqua fortis, makes the water of a green colour; and on pouring to this the two lixivia of blood and of flesh, the coagula are much alike; that is, they are white, tinged with green; but on adding spirit of salt to them, they become of a colour not unlike that of copper before the solution. Oil of tartar gives a pale green solution; and the spirit of salt clears up the liquor, and restores it to its former colour.
Bismuth dissolved in aqua fortis, and mixed with a lixivium of blood, produces a milky coagulum, which, after a short time standing, with the addition of some spirit of salt, becomes of a pale blue. The lixivia of flesh, and of crude salt of tartar, produced both white coagula, which the spirit of salt made no alteration in. From these experiments it appears, that not any of these metallic bodies would produce a fine blue colour with the lixivium of the blood; but a solution of iron answers all the experiments that are made with the solution of vitriol, and produces as fine a blue colour as that made in the common way.