^cid of Lemons prepared in the Large Way. 43 



XIIL 



On tie Preparation of concrete Aid of Lemons. By DiZEy Apothecary in Chief to the French 

 Jrmy, charged -with the InfpeBion efthe General Magazine of Medicines *. 



X HOUGH nature prefents us with the citric acid nearly in a difengaged ftate, it is 

 neverthelefs confounded in lemon juice with an extraftive mucilaginous matter, which op- 

 pofcs the union of its cryftallizable particles, and which cannot be feparated by the fimplc 

 procefs of evaporation and expofure to cryftalllze. 



Scheele was the iirft who obtained this acid in the foHd form. In the year 1774, Georgius 

 in Sweden, and afterwards Du Buiflbn in France, publiflied obfervations on the method of 

 concentrating and preferving lemon juice. Although their labours, as well as the experi- 

 ment of Stahl and Guyton, could not determine the cryftalllzation of this acid, it is never- 

 thelefs certain that their refearches were very ufeful to affift Scheele in his difcovery of tht 

 procefs he has left us. 



I availed myfelf of an opportunity to repeat the procefs of Scheele in the large way, ani 

 to infift on an eflentlal obfervation, which that chemift has not fufEciently developed } for 

 it is one of tlie neceflary conditions for fuccefs in the cryftallization of this vegetable acid. 

 Scheele, after feveral unfavourable attempts, advifes the feparation of the extraftive and 

 mucilaginous matter of lemon juice, by uniting the citric acid to thebafis of calcareous car- 

 bonate, with which it forms a citrate of lime, that precipitates on account of its fparing fo- 

 lubllity, while the extractive and mucous matter remains diflblved in the fluid. This citrate 

 of lime is afterwards decompofed by a fufficient quantity of fulphuric acid diluted with 

 water, with the precaution to add an excefs of this laft acid. The fulphuric acid feizes the 

 lime from the citric acid, and forms a fulphate, -which falls to the bottom becaufe nearly 

 infoluble ; while the citric acid, being fet at liberty, is diflblved in the water with which 

 the fulphuric acid was diluted. 



Filtration and wafliing with cold water feparate the citric acid entirely from the fulphate 

 of lime, and it may be afterwards obtained in the concrete ftate by evaporation in ftone- 

 ware veflels, at the temperature of boiling water. I have oWcrved that it is very ufeful to 

 •fufpend the evaporation every two days, in order to permit the fulphate of lime, which is 

 fufpended by the afliftance of the citric acid, to fall down. 



The citric acid which I have prepared is the produd of feveral chefts of lemons. Thfc 

 mafs of calcareous citrate which was decompofed was fomewhat confiderable, and the ope- 

 ration was performed in large ftone-ware veflels. The fulphate of lime obtained by the de- 

 compofition of the calcareous citrate was well wafhed in tubs of white wood. The dif- 

 ferent liquors were united together for evaporation in ftone-ware veflels, at the tem- 

 perature of boiling water. They were clear, light-yellow, and contained an excefs of ful- 

 j)huric acid. 



As foon as the liquors were fufficiently concentrated by evaporation, the fulphuric acid 

 exerted its aftion, and the yellow colour became brown, and even blackifli at the end of 



• Read to the National Inftitute of France, and copied in the Journal de Phyfique, publiflied to fupply the 

 iefeft of the numberfot September 1794. 



G% Out 



