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and will no longer liquefy in the fire. For this purpose,a quantity of the vitriol may be put into an iron pot, suchas one of those which are used as sand-pots for the por-table furnaces already described : The vessel is set over agentle fire, which is gradually increased when the vitriolmelts, till the matter thickens again, and acquires an ashgrey colour : the vitriol is to be constantly stirred, tillit becomes dry and powdery, and is then to be takenout whilst hot; for if suffered to cool in the vessel, with-out stirring, it concretes so hard, as scarce to be beatenoff with a hammer. Some calcine the vitriol in anearthen pan : the pan is at first about half filled, and whenthis has funk down, and incrustated about the sides, moreis added, till the vessel is full, which must afterwards bebroken for getting the matter out.

Eight pounds of vitriol thus calcined to about four, andthree pounds of nitre made likewise very dry, are to bereduced separately into very fine powder, and thoroughlymixed together. The mixture is to be put into the sameiron pot in which the vitriol was calcined, a stone-warehead with a large glass receiver fitted to it, and the junc-tures luted with Windsor loam, or a mixture of clay andsand, beaten up with some cut tow, and moistened witha solution of fixt alkaline salt. In the receiver may beplaced a pint of water, which will promote the condensa-tion-of the nitrous fumes, without rendering the acid toodilute for the purposes which it is here designed for.During the distillation, there arises a quantity of elasticvapour, which must be suffered to escape, as it wouldotherwise either force the luting, or burst the receiver.The most convenient way of procuring an outlet for it,without endangering any loss of the acid, appears to be,by making a hole in that part of the receiver which is tobe placed uppermost, and inserting into it a slender glass

pipe.