These experiments seem therefore to support the fourth proposition, and to shew that the caustic alkali does not contain any lime.
As it seems probable, from the quickness and ease wherewith the alkali was rendered caustic, that more lime had been employed than what was just sufficient to extract the whole of its air, we are surprised to find that little or none of the superfluous quick-lime was dissolved by the water. But this _phænomenon_ will become less surprizing, by comparing it with some similar instances in chemistry. Water may be made to deposite a salt, by the admixture of a substance which it attracts more strongly than it does that salt; such as spirit of wine; and quick-lime itself may be separated from water upon the same principle; for if that spirit is added to an equal quantity of lime-water, the mixture becomes turbid and deposites a sediment, which, when separated and dissolved again in distilled water, composes lime-water. We may therefore refer the above _phænomenon_, with respect to the ley, to the same cause with these, and say, that the water did not dissolve the lime, because it already contained a caustic alkali, for which it has a superior attraction.
I also rendered the volatile alkali caustic, in order to examine what change it suffered in the operation, and obtained an exceedingly volatile and acrid spirit, which neither effervesced with acids, nor altered in the least the transparency of lime-water; and, altho' very strong, was lighter than water, and floated upon it like spirit of wine.
I next inquired into the truth of the fifth proposition, in the following manner.
Two drams of epsom-salt were dissolved in a small quantity of water, and thrown into two ounces of the caustic-ley; the mixture instantly became thick, like a decoction of starch or barley, by the magnesia, which was precipitated. I then added spirit of vitriol by degrees, until the mixture became perfectly clear, or the whole of the magnesia was again dissolved; which happened without any effervescence or emission of air.
Half an ounce of chalk was dissolved in spirit of salt, the quantity of which was so adjusted, that the mixture was not acid in the least degree; and the solution was thrown into twelve ounces of the caustic ley; which quantity I found, by experiment, to be sufficient for precipitating almost the whole of the chalk. I now filtrated this turbid liquor, and laid the powder remaining in the paper upon a chalk-stone, in order to draw as much of the water from it as possible, and thereby reduce it to the form of a more dense and heavy powder, that it might subside the more perfectly in the following part of the experiment. I then mixed it with about twenty ounces of pure water in a flask, and, after allowing the powder to subside, poured off the water, which had all the qualities of lime-water. And I successively converted eight waters more into lime-water, seven of these in the same quantity, and with the same management, as the first. The eighth was likeways in the same quantity; but I allowed it to remain with the chalk, and shook it frequently, for two days. This, after being filtrated, formed a cream or crust upon its surface when exposed to the air; changed the colour of the juice of violets into green; separated an orange-coloured powder from a solution of corrosive sublimate; became turbid upon the addition of an alkali; was entirely sweetened by magnesia; and appeared so strong to the taste, that I could not have distinguished it from ordinary lime-water. And when I threw some salt ammoniac into the lime which remained, the vapour of the volatile alkali immediately arose from the mixture.