a fixed alkaline salt, prepared chiefly in Germany, Russia, and Poland, by melting the salts out of the ashes of burnt wood; and having reduced them again to dryness, evaporating the moisture, and calcining them for a considerable time in a furnace moderately hot. The goodness of pearl-ashes must be distinguished by a uniform and white appearance, they are nevertheless subject to a common adulteration, not easy to be distinguished by the mere appearance: which is done by the addition of common salt. In order to find out this fraud, take a small quantity of the suspected salt; and after it has been softened by lying in the air, put it over the fire in a shovel: if it contains any common salt, a crackling and slight explosion will take place as the salt grows hot.

Pearl-ashes are much used in the manufacture of glass, and require no preparation, except where very great transparency is required, as in the case of looking glass, and the best kind of window-glass. For this purpose dissolve them in four times their weight of boiling water: when they are dissolved, let the solution be put into a clean tub, and suffered to remain there 24 hours or more. Let the clear part of the fluid be then decanted off from the sediment, and put back into the iron pot in which the solution was made; in this let the water be evaporated till the salts be left perfectly dry. Keep those that are not designed for immediate use in stone jars, well secured from moisture and air.

Mr Kirwan, who instituted a set of experiments on the alkaline substances used in bleaching, &c. (see Iris Transact. for 1789), tells us, that in 100 parts of the Dantzig pearl-ash, the vegetable alkali amounted to somewhat above 63. His pearl-ash he prepares by calcining a ley of vegetable ashes dried into a salt to whiteness. In this operation, he says, "particular care should be taken that it should not melt, as the extractive matter would not be thoroughly consumed, and the alkali would form such a union with the earthy parts as could not easily be dissolved." He has added this caution, as Dr Lewis and Mr Duffie have inadvertently directed the contrary." We apprehend, however, that here is a little inaccuracy; and that it was not for pearl-ash, but for the unrefined pot-ash, that these gentlemen directed fusion. The fact is, that the American pot-ashes, examined by them, had unquestionably suffered fusion; which was effected in the same iron pot in which the evaporation was finished, by rather increasing the fire at the end of the process: by this management, one of the most troublesome operations in the whole manufacture, the separation of the hard salt from the vessels with hammers and chisels, was avoided; and though the extractive matter was not consumed, it was burnt to an insoluble coal; so that the salt, though black itself, produced a pale or colourless solution, and was uncommonly strong. Mr Kirwan has also given tables of the quantities of ashes and salt obtained from different vegetables; and he concludes from them, 1. "That in general weeds yield much more ashes, and their ashes much more salt, than woods; and that consequently, as to salts of the vegetable alkali kind, neither America, Tricife, nor the northern countries, possess any advantage over us. 2. That of all weeds, fumitory produces most salt, and next to it wormwood; but if we attend only to the quantity of salt in a given weight of ashes, the ashes of wormwood contain most. Trifolium fibricum also produces more ashes and salt than fern." See POTASH.