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■when it has attained its full growth, (which becaufe this employment is carried on rather ashappens about the middle of July) is cut down, fubfidiary to clearing the ground for agricul-and after being half-dried in the open air, is ' '

gathered into fmall heaps and kindled. The com-buftion proceeds flowly, being accompanied by

a fmothering fmoak and little or no flame, tillthe whole is reduced to a reddifh grey alh: thisbeing carefully collected is fprinkled with alittle water., and then moulded by hand intoballs from three to four inches in diameter,which when they have acquired a certain hard-nefs and folidity by drying in the fun, are readyfor fale. In Ireland , thiftles, docks and weedsof all kinds are mixed with the fern, and thealhes are difpofed of in their loofe pulverulentftate without any further preparation. Accord-ing to Dr. Home fern-afhes contain about -5- oftheir weight of fait, conlifting principally offub-carbonat and fulphat of potafh. 1000 partsof the plant cut in Auguft, and thoroughlydried, afford 36.46 of alhes, from which areobtained by lixiviation 4.25 of fait. The com-mon Irilh weed alhes have been analyzed byMr. Kirwan; and when deprived of their waterby a red heat appear to contain x part of faitfor 3I .parts of alh; of this the free alkalineportion however, as deduced from the quan-tity of alum decompofed by the lixivium, a-mounted only to yV of the whole. 0

The potafo of commerce, or black potajh, as itis alfo called, is univerfally procured from thecombuftion of wood; and therefore its prepara-tion can only be undertaken with fuccefs inthofe uncleared countries in which are vaftnatural forefts, and where from the badnefs ofroads, and imperfection of water communica-tion, the value of timber is no more than that ofthe labour employed in felling it. The onlydiftriCts in Europe in which any confiderablequantity of potafh is made, are the mountain-ous forefts of Germany , and the extenfivewoodland trafts of Poland and Ruffia. TheBritifh market however is principally l'uppliedfrom the United States of North America j acountry in which from its rapid increafe inpopulation there is a conftant demand forcleared land for the purpofe of cultivation, andtherefore timber is looked upon rather as anincumbrance, than as contributing either to thebeauty or value of the ground on which itHands.

The moll wafteful method*of manufacturingpotalh is that praCtifed by the Americans,partly on account of the ignorance of thepeople by whom it is prepared, but principally

c Irilh Tranfaflions.

ture than on its own account. The wood asfoon as it is fufficiently dry to burn is collectedinto large piles and reduced to afhes: thefeallies are then put into a wooden ciftern, witha plug at the bottom of one of the fides, and aquantity of water fufficient to make a ftronglixivium is added: after Handing for an hour or •two the plug is withdrawn, and the waterholding the potafh in folution runs clear out,leaving the earthy part ftill impregnated withalkali in the ciftern. This folution is then eva-porated to drynefs in iron pans, and haftilyfufed into compact reddifh brown maffes offemi-cauftic potafh, in which ftate it is fit forthe market.

In Germany , where potafh is prepared on itsown account, and where a greater degree ofintelligence and economy is praCtifed, the gene-ral method of proceeding is the fame as thatjuft mentioned, but with fuch variations as,though feemingly of little confequence, materi-ally augment the produce of alkali. Care, istaken to felect fuch kinds of wood qs are thericheft in potalh; the combuftion is flower, andof courfe the temperature lower, in confequenceof which but little is loft by volatilization; thelixiviations of the afhes are alfo judicioufly re-peated till the whole of the alkali is extracted.

The common Ruffian potafh is the impurellof all, containing nearly one half its weight ofearth, and is thus prepared. A large pit is dug,into which are thrown burning brands and thefmaller extremities of the branches, and whenthe whole is well kindled the pit is filled upwith logs and other large pieces, which at length,though very flowly, are reduced to afhes. Thecoarfer part of the allies is then feparated bylifting from the finer; all the alkali that it con-tains is procured by lixiviation; and this liquoris mixed with the remainder of the alhes andworked together into a kind of pafte. A pile isthen built of alternate ftrata of wood and thispafte, and being fet lire to the whole is again re-duced to alhes. This procefs is repeated feveraltimes till the alhes begin to clot and become hard:the moll compaCt pieces being then feleCted,are packed up for fale without any further pre-paration ; the reft are lixiviated and boileddown to drynefs in the ufual manner.

In fome parts of Germany potalh is madefrom the empyreumatic acid produced fromwood while burning into charcoal. By meansof wide tubes of plate iron or copper, the acid