C IT
C IT
( 292 )
Lemon Juice Chalk Citrat of Lime Citric Acid Citric Acid
in cryftals
loolb. requires 4.251b. and produces 7.511b. yields 4.381b. and contains 4.741b. Prouft.for by by by
— faturation 4.65— precipitation 8.0—evaporation 3.90—> eftimation- Weftrumb*
-- 6.25— 20. —— 6.25— Dizi.
Cry ft.
Citric A.
6.25 6.25— 9.375 „ D°
With regard to the proportions given byProuft, it is to be obferved that only 7.51 ofcitrat of lime was actually precipitated, but byevaporation of the liquor he obtained aboutadditional, or .541b. The cryftallized acid wasobtained from a known quantity of the wafhedcitrat of lime, 6 ounces of the latter giving 34of the acid, hence 7.51 lb. would yield 4.38 lb.the .541b. of the citrat procured by evaporationwould therefore yield .315 of the cryftallizedacid, which, added to 4.38 gives 4.695 for thequantity of acid, exclufive of the fmall portionleft in the laft liquor after all the cryftals havebeen removed, which the author eftimates at alittle more than of the quantity obtained,or in the prefent inftance about .044, making atotal of 4.74 of folid acid in 100 of the frefhjuice.
The quantity of fulphuric acid required forthe decompofition of the citrat is variouflyeftimated, and as an excefs of it is requifite, atleaft as much of the concentrated acid as willbe equal to the chalk employed may be ufed,diluting it with about ten times its bulk ofwater. In this preparation therefore as theftrength of the lemon juice is uncertain, and, asit would appear, the product of citrat of limeequally fo,and troublefome to eftimate,the quan-tity of chalk ufed feems the only proper guideto determine that of the fulphuric acid demanded,and the probable yield of citric acid. There-fore the chalk fhould be weighed, and thequantity ufed fhould be noted, which fhould bea little more than to faturation to engage thewhole of the citric acid. If a portion of thefame chalk be previoufly and feparately mixedwith fome of the fulphuric acid intended to beufed, and the quantity required for faturationhe obferved, it will furnifh a ftill better guidefor the fecond part of the procefs than that oftiling equal weights of chalk and acid. Theclear fupernatant liquor contains, befides themucilage and extract, a portion of malat oflime in folution, lemon juice containing a fmallquantity of the malic acid. This calcareous
fait is precipitated by alcohol, if the liquor isconcentrated by evaporation. A minute portionof gallic acid alfo appears in lemon juice by theteft of iron, the mixture turning of a brownred after being faturated with an alkali.
To feparate the citric acid compleatly fromthe lime, by the fulphuric in the fecond ftep ofthe procefs, Prouft recommends boiling thewhole for about five or ten minutes. The dif-ficulty of feparating all the fulphat of lime andextract from the difengaged citric acid, and ofprocuring clear regular cryftals has already,been mentioned. A little alcohol added towards-the end of the firft evaporation, and fubfidencefor fome hours greatly affifts this feparation,,and in the perfection of the cryftals.
Richter gives another procefs for preparingthe citric acid, k which may be mentioned,though it does not appear that it is much ufed.Saturate lemon juice with carbonat of potaili,then add fufficicnt acetited lead. A copiouswhite precipitate appears, which is the citrat oflead. When no more falls down, walh theprecipitate, digeft with dilute fulphuric acid (asin the former procefs) to difengage the citricacid, evaporate the liquor to a thick confiftence,,add a few drops of nitric acid, and cryftallize.
The theory of this operation is the fame as inthe former inftance, fubftituting lead for lime,and with this difference that the lemon juice-muft firft be faturated with alkali that the ace-tite of lead may be decompofed by double affinityby the citrat of potafh, and to prevent an excelsof acid by which the citrat of lead is rendered 1very folubiej though without fuch an excefs itis fcareely diffolved in any fenfible degree. :Where this acid is ufed for the table the- intro--duct ion of fo dangerous a metal as lead, parti-'cularly in its acid combinations, is a^-ferious;objection, and for manufacture it appears moreexpenfive than in Scheele ’s method.
Lemon juice when imported in'this ftate isnot unfrequently adulterated with fome ftrongand cheaper acid. The fulphuric is moll to befufpected. It is detected in the following way .