[ 15 ] terials which yield Nitre, is put into a large copper vessel, and is gradually boiled away till crystals of common salt begin to form in it. These are taken out with a large laddle as fast as they form and thrown into a large basket which stands directly over the vessel in which liquor is boiling. When no more crystals of common salt can be found, the liquor is taken off the fire, and emptied into a number of copper-pans, in a cellar, in which it soon shoots into crystals of Salt-petre. The salt has now undergone its degree of purification. As a quantity of common salt still adheres to the crystals of Nitre, it is necessary to dissolve them in pure water, and boil them in the manner we laid before. A much less quantity of common salt is obtained now than formerly. The Nitre, after its second crystallization, is used chiefly for the purposes of medicine and curing provisions. But there is a third degree of purification necessary, before all the common salt can be completely separated from it. It is carried on in the same manner as the former ones were. The salt-Petre is now in its highest state of purity, in which state only it is used for the manufactory of GunPowder. The liquor which will not crystalize may be used for making Magnesia. I cannot conclude this Memoir without observing that the climate and productions of the middle and northern colonies of America, render them extremely proper for the manufactory of Salt-Petre, and the success which has attended several experiments in that way, give us reason to believe that it may be carried on in this country, with as
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