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equally jnfoluble with the citrat, whilft thecitric acid, now fet free, remains diflolved inthe clear liquor, and by due evaporation maybe procured pure, and in large cryftals. Thefulphuric acid fhould be a little in excefs to en-gage all the lime, otherwife the acid will notcryltallize.

Such is the procefs of this excellent chemift,but as the preparation of this acid has latelybecome an objeCt of fome importance in manu-facture, it may be of advantage to compare theparticulars of the procefs as given by differentchemifts.

In preparing citric acid in the great way,M. Dize £ mentions the following particulars.After the citrat of lime has been decompofed bythe fulphuric acid, cold water afhfted by ftirringis fufficient to wafh out all the citric acid ad-hering to the fulphat of lime. This is of ufeboth as faving fuel and as lefs of the calcareousfulphat is diflolved. Much however is ftill con-tained in the clear liquor, which in faCt is amixture of citric acid with the excefs of ful-phuric acid which it is neceffary to add, andfulphat of lime held in folution. This liquormay be evaporated at a heat of boiling water.It is is a clear light yellow. As the bulk of li-quid diminifhes, the fulphat of lime falls down,and it is of ufe to fufpend the evaporation onceor twice for fome hours, that by cooling thewhole of the fulphat may be depofited. To-wards the end, the liquor becomes blackilhowing to the fulphuric acid becoming con-centrated, and aCting partly perhaps on theacid itfelf, and partly as the author imagines,on a portion of extractive matter, which fub-fides along with the citrat of lime, and whichhe thinks it is neceffary to deftroy in this man-ner before the citric acid will cryltallize. Thisacid is fo very foluble that the evaporationmull be pulhed to a very thick fyrupy con-fiftence before the cryftals will feparate. Theyare at firft black and dirty. By re-folution incold water (of which a fmall quantity will fuf-fice) by filtration, and a fecond evaporation,they become yellow and more regular. Athird cryftallization feems neceffary to makethem white and pure. As there is much wafte

in thefe operations, the foul portion which willnot pafs the filter fhould be evaporated andtreated as before.

Scheele has well remarked (and all otherchemifts have found the fame) that an excefsof fulphuric acid is required. M. Dize fup-pofes the peculiar ufe of this excefs to be todeftroy the remaining extractive matter, theexiftence of which he endeavours to prove bythe proportions of ingredients required, andtheir produCts. One hundred pounds of thelemon juice he found to require for faturation6.25 lb. of chalk, and to produce as much as20 lb. of citrat of lime. On the other handhe found the cryftallized citric acid to requireits own weight of chalk for faturation, and toproduce a quantity of citrat of lime equal tothree-fourths of the weight of the two ingredi-ents, the lofs being chiefly carbonic acid.Hence he concludes that 100 lb. of frefh juicecontains 6.25 lb. of the pure acid (that is equalin weight to the chalk required), and that thecitrat of lime thence refulting if pure, aught tobe no more than 9.378 lb. (being three-fourthsof the fums of the weight of the chalk, and thefuppofed quantity of pure acid). But as it isreally 20 lb. even after walhing, he fuppofesthis enormous difference to be made up byextractive matter precipitated along with thecitrat of lime, and adhering to it. Howeverthe refults of the experiments of other chemiftsdo not give this difference, though they agreetolerably in other particulars. M. Dize doesnot fpecify the quantity of cryftallized acidactually obtained from a given quantity ofjuice.

Weftrumb h faturated 4lb. of frefh lemonjuice, Amply {trained, with 3 ounces of chalk,and obtained 5 oz. and 1 dram of citrat of lime*which, decompofed with 23 drams of ftrongfulphuric acid diluted with about ten times itsbulk of water, gave by due evaporation 24-ounces of cryftallized acid a little foul, whichloft one dram by a fecond cryftallization.

Profeffor Prouft has examined the fame pro-cefs.* The ingredients and products given bythofe three chemifts, reduced to the fame pro-portion, are as follows:

* Journ. de Phyf. k Leonhardi in Jlacrjuers Worterbuch Art. Citronenfaure. • Jour, de Phyf.