POTASH, the lixivious ashes of certain vegetables, used in making of glass, soap, &c. See GLASS, SOAP, &c.
The method of making potash is directed by Dr D. Shaw as follows. Burn a quantity of hilt-wood to method of making potash. grey ashes; and taking several pounds of these ashes, boil them in water, so as to make a very strong lixivium, or ley. Let this ley be strained through a coarse linen cloth, to keep out any black parts of the half-burnt wood that might happen to remain in the ashes; then evaporate this strained ley in an iron-pan over a quick fire almost to dryness: then taking out the matter remaining
Potash. maining at the bottom, and putting it into an iron crucible, set it in a strong fire till the matter is melted, and then immediately pour it out upon an iron-plate, where it soon cools, and appears in the form of a solid lump of potash*. Much after this manner is pot-ash made in the large way of business, for the service of the soap-boiler, glass-maker, fuller, &c. but according to the difference of the wood, or combustible matter employed, with the manner of turning it, and conducting the process, different kinds of potash are prepared. There are certain saline plants that yield this potash to great advantage, as particularly the plant kali; there are others that afford it in less plenty, and of an inferior quality, as bean-stalks, &c. but in general, all vegetable subjects afford it of one kind or other, and may most of them be made to yield it tolerably perfect after the manner of the process already laid down, even the loppings, roots, and refuse parts of ordinary trees, vine clippings, &c. The fixed salts of all vegetables excepting the kali and marine plants, when reduced to absolute purity, or entirely separated from the other principles, appear to be one and the same thing: whence it should seem, says Dr Shaw, that by a suitable management, good salable potash might be made in all places where vegetable matters abound. For if by examining Russia (A) potash, for example, we find that its superiority depends upon its being clear of earth, or upon its containing a large proportion of oil, or refined salt, these advantages may, by properly regulating the operation, be given to English potashes, so as perhaps to render the latter as good as the former: but where the potash of any remarkable saline vegetable is to be imitated, that of the kali, for example, the Doctor recommends a prudent sprinkling of the subject with salt, or sea-water, in the burning; and by these ways, properly diversified, any principle that is naturally wanting might be artificially introduced so as to perfect the art of potash.
Account of Mr Stephens's manufacture. About 40 years ago or upwards, Mr Stephens, encouraged by the Society of Arts, &c. and by a parliamentary grant of 3000l. established a manufacture of pot-ash in North America, which produced such as was so perfectly good as to answer in bleaching and other uses the purposes of pearl-ash; and which at the same time afforded a very large produce. But the very great heat which his process required, occasioned the destruction of a very extensive apparatus; and other circumstances concurred to disappoint the hopes and check the spirit of the proprietors. The manufacture was, however, afterwards undertaken and prosecuted by others.