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thofe acids and other vegetable principles withwhich it was before united. The former ofthefe opinions was adopted by Macquer andmany of the eminent chemifts that were con-temporary with him, but of late the latter opi-nion has been rather gaining ground. Theprincipal arguments by which Macquer fupportshis theory are the following d . ill. When vege-tables, capable of furnilhing much alkali bycombuftion, are deeompofed in any other way,no other faline products are obtained but liquidand concrete acids. 2d. When vegetables aredeprived of part of their acid by diftillation theproduce of alkali is proportionately diminilhed.3d. The concrete acids, as tartar, are changedinto alkali merely by combuftion. 4th. Plantsthat yield little or no acid in diftillation arefound after combuftion to afford little alkali.5th. Plants, which when burnt without anyprevious alteration, yield much alkali, if burntafter undergoing compleat putrefaftion, affordno alkali.
In oppofition however to thefe arguments itmay be obferved, ill. That the native concreteoxalic, and tartareous acids have been proved bymodern chemifts to be acidulse, or in otherwords to contain potafli, though not to full fa-turation of the acid •, and therefore when thefeare burnt no converfion of acid into alkali takesplace, but the acid being volatilized and decom-pofed, the alkali which was before malked byan excefs of acid now exhibits itfelf with itsufual characters. 2d. Nitre eompleatly formedhas been difcovered in borrage and fame othervegetables, therefore the exiftence of potafh, thealkaline bafe of this fait, is alfo neceffarily de-monftrated. 3d. Vauquelin has fhown that the
found in the market would no doubt on analyfi#afford very different refults, efpecially with re-gard to the proportions of earthy matter, ofwater, and of carbonic acid •, it is not thereforeperhaps much to be regretted that we poffefs novery accurate analylis of any of them. Theonly one on which any reliance can be placed isof Dantzic pearlafh by Mr. Kirwan, f in whichare contained about
60.3 potafli
22.4 carbonic acid7.2 water
8.7 fulphated potalh0.7 muriated ditto0.7 earth
100.0
But if the analylis of any particular fample isof little confequence generally fpeaking, y e t itis of confiderable inportance both to the manu-facturer and chemift, to be in poffeffion of acompendious and accurate mode of afcertainingthe contents of the various kinds of pot andpearlafh, in order to make advantageous pur-chafes of articles, in the intrinlic worth of whichthere is fo much difference,
Mr. Kirwan’s method of calculating the pro-portion of real alkali, in a given lixivium, fromthe quantity of precipitate which it throwsdown from a folution of alum, is by no meansto be depended on; for in the firft place thefilex and alumine which the lixivium holds infolution, are precipitated together with theearth of alum; and in the fecond place fo muchdepends on the degree of waffling and calcina-
tion which the precipitate is made to undergo,fap of trees contains acetite of potafh. 4th. The that from equal quantities of alum it is fcarcelyreafon why vegetables after putrefaction yield poflible to obtain equal weights of earth. Upon
no alkali is that their texture being broken upby this procefs, the water which drains throughthe mafs diffolves and carries off all the alkaliwhich they at firft contained. This is manifeftfrom the experiments of Mr. Birch,' who, byevaporating and calcining 24 wine-pipes, or3024 gallons, of dunghill water, procured1048 lbs. of good marketable potafli. We maytherefore conclude that the potafh obtained bylixiviation of vegetable allies pre-exifted in theplants themfelves: whether this alkali is formedduring the procefs of vegetation, or is onlyimbibed from the earth by the roots, is not asyet determined.
The varieties of pot and pearlafn which are
* Exaailn. of the alkaline fubilances ufed in bleaching.
the whole therefore perhaps the beft mode ofproceeding is as follows.
1 ft. Prepare a diluted fulphuric acid by mix-ing the concentrated acid, called oil of vitriol,with three times its bulk of diftilled water.Then tell it by taking 100 grains of the dilutedacid, and adding muriat of barytes as long as anyprecipitate falls down. The fulphat of barytesthus prepared when wafhed with cold water, anddried at a low red heat, contains 33.3 per cent, offulphuric acid, hence the real acid in any quan-tity of the diluted acid is readily afeertamed.
2d. Pulverize 500 grains of the alkali underexamination, and digeft it in warm water, add-ing frelh portions of this fluid as long as any
Phil, tranf. for 1780, p. 34 S’