PHARMACY, no 479, 751, 754, 755, 756, 757, 758, Quicksilver 759, 760, 761, 762, 763.
Mercury may easily be cleansed from those extraneous matters which adhere only slightly to it, by making it pass through a new, clean, and close cloth, and afterwards by heating it. When mercury has been thus purified, and is free from all metallic alloy, it is considerably fluid. A phosphoric light is produced by shaking in the dark such mercury contained in a barometer. Its integrant parts, like those of melted metals, seem mutually to attract each other, and always acquire a convex or spherical form when they touch bodies with which they have no tendency to unite.
A new method of purifying quicksilver from lead has been discovered by Dr Priestley; of which he gives the following account.
"I take a glass phial with a ground stopper (such being generally pretty strong) containing 10 or 12 ounces of water, and fill about one-fourth of it with the foul quicksilver; then, putting in the stopper, I hold it inverted with both my hands, and shake it violently, generally striking the hand that supports it against my thigh. When I have given it 20 or 30 strokes in this manner, I take out the stopper, and blow into the phial with a pair of bellows; which I do in order to change the air that has become in part phlogisticated, and knowing that the purer the air is the faster the process advances.
"After a short time, if the mercury be very foul, the surface will not only become black, but a great quantity of the upper part of it will be, as it were, coagulated, so as to be easily separated from the rest. I therefore invert the phial; and covering the mouth of it with my finger, let out all the mercury that will flow easily, and put the black coagulated part into a cup by itself. This I press repeatedly with the end of my finger, till I make a complete separation of the running mercury from the black powder; and putting the powder by itself, I pour back the mercury to the rest of the mass out of which it was taken, in order to be agitated with it again.
"This process I repeat till I find that no more black matter can be separated; and it is not a little remarkable, that the operator will be at no loss to know when the process is completed. For the same quantity of lead seems to come out of it in equal times of agitation, and consequently the whole becomes pure at once. Also, whereas, while the lead was in the mercury, it felt, as I may say, like soft clay, the moment the lead is separated from it, it begins to rattle as it is shaken, so that any person in the room may perceive when it has been agitated enough (A).
"That the mercury is made quite pure by this process I ascertained by distillation. For having distilled in a glass vessel a large quantity of quicksilver, in which both lead and tin had been purposely dissolved, and which had only been agitated in this manner afterwards, I found nothing more than a light whitish stain on the bottom of the retort.
"When a quantity of the black powder is procured, it
Quicksilver. it is very easy, by distillation, to separate the mercury from the calx; and I do not know a readier method of procuring the calx of lead, or tin, and perhaps the calx of other metals also. The quantity of black mercurial powder is very considerable in proportion to the lead or tin mixed with it; though it is not easy to ascertain this with exactness, because, in endeavouring to separate the powder from the running mercury, a good deal of it is, by mere trituration, converted into running mercury; and I do not know but that, in time, the whole might be restored by this means, and the calx of lead, &c. be got quite pure. However, from the following experiments it will be seen what proportion they generally bear to each other, after a tolerably careful separation. It will be seen also, that when all the quicksilver that was converted into black powder is expelled from lead or tin by heat, there will remain more weight of the calx than there was of the metal; as might be expected. But as I applied more heat than was necessary to separate the quicksilver, a good deal of the air, and whatever else contributes to the additional weight of the calx, is, no doubt, expelled with it.
“Having mixed 1 dwt. of lead with about five pounds of quicksilver, I expelled it all by agitation, in the method described above; when, weighing the black powder, it was found to be 1 oz. 10 dwt. 5 gr. some particles of the running mercury being, however, still visible in it. When the quicksilver was expelled by heat, the calx of the lead appeared in the form of a brownish powder, and weighed 1 dwt. 5 gr.
“Having mixed 1 dwt. of tin with the abovementioned quantity of quicksilver, and having expelled it again by agitation, the black powder, with some small globules of quicksilver mixed with it, weighed 2 oz. 1 dwt. 5 gr. and the calx, which was a tolerably white powder, weighed 1 dwt. 7 gr.
“The separation of tin from quicksilver by agitation is not effected near so soon as lead. It requires at least four times the labour. It also requires proportionably more time to separate the black powder from the thick amalgam, in the manner described above.
“Quicksilver is separated from lead or tin when the mass is agitated in water, as well as in air; but it seems to require more time. In this process it is also easily perceived when all the base metal is expelled; the phenomena of the agitation of this amalgam and of pure mercury in water being very remarkably different. It is even easy to perceive, by this means, in a moment, whether the quicksilver be pure or not. For if it be impure, the water becomes opaque the moment the agitation commences; which is by no means the case with pure quicksilver, especially if the water in which it is agitated has not been used for this purpose before. Also, the black matter suspended in the water in which pure quicksilver has been agitated is (except in a case that will be described hereafter) presently deposited; whereas the water in which the amalgam has been agitated does not become clear in several days. It may also be perceived how the quicksilver approaches towards purity, by this deposit being made more or less readily.
“Also, the phenomena during the agitation in Quicksilver these two cases are strikingly different, tho' not easily described in words. More especially, the mixture of quicksilver with lead or tin does not seem to admit the water to mix with it; whereas pure quicksilver, by violent agitation, may be so thoroughly mixed with the water, that it will sometimes be several seconds after the agitation is discontinued, before it have entirely disengaged itself from the water; and in doing this it exhibits a very pleasing spectacle. By this means, as in the process without water, it may be perceived at once when the separation of the base metal and the mercury is completely effected.
“Having a large quantity of water made very black with the agitation of a mixture of quicksilver and lead, I agitated a quantity of common air in it a long time, and let it stand several days; but the air was not sensibly injured by this means; so that though this water and the calcined amalgam suspended in it do contain phlogiston, it is not by this means imparted to the air.
“I evaporated a pint of the distilled water in which quicksilver and tin had been agitated, and which had stood till it was quite transparent, when a white sediment remained, but it did not weigh more than a few grains.”
By long agitation in water, the purest quicksilver will be converted into a black powder. The process succeeds best when as much water is used as is three or four times the bulk of quicksilver. This black matter, however, is not permanent, but becomes running mercury by being merely exposed to the air, without trituration, or any other kind of operation. Spirit of wine answers the purpose as well as water; and the appearance seems to be occasioned by a small quantity of superfluous phlogiston adhering to the metal.