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. In this experiment therefore the air is first driven out of the chalk by an acid, and then, in order to separate this acid from it, we add an alkali which has been previously deprived of its air; by which means, the chalk itself is also obtained free of air, and in an acrid form, or in the form of slaked lime. We have also several processes for obtaining the volatile alkali in a caustic form, which seem to be only so many methods of obtaining it in its pure state, and free of fixed air. The first of these is the separation of the alkali from an acid, merely by heat; an instance of which we have from Mr. _Margraaf_.[9] He prepared from urine an ammoniacal salt, the acid of which is the basis of the phosphorus, and is of such a peculiar nature, that it endures a red heat without being dissipated. Sixteen ounces of the neutral salt were subjected by him to distillation. The acid remained in the retort, and he found in the receiver eight ounces of an alkaline spirit, which, he tells us, was extremely volatile, very much resembling the spirit of salt ammoniac distilled with quick-lime; and no crystals were formed in it, when exposed to the cold air.