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XIX. Refcarchcs rcfpe&ing the Preparation of the Citric Acid, 

 By Profejffbr Pkoust. 



V-7NE of my friends, Don Antonio Hernandez del Valle, 

 fecretary to the confulfhip of the Havannah, wrote to me in 

 the year 1795, during his refidence at Cadiz, before he em- 

 barked, to requeft fome information refpecting the beft me- 

 thod of preferving lemon juice during long voyages ; a pro- 

 cefs in which no one had ever yet properly fucceeded. As 

 his acquaintance with chemiftry infpired him with a defign 

 to make experiments on this fubjeft, he defired me to make 

 fome refearches, that he might compare them with thofe he 

 propofed to undertake in regard to this acid as foon as he 

 mould reach the place of his deitination. 



What I am going to fay on the fubjecl: will make no ad- 

 dition to our knowledge on the nature of the acid of lemon- 

 juice, fince the indefatigable Scheele has left nothing to be 

 wifhed for on this fubjecl; I only intend to reduce to fixed 

 data his formula for the extraction of this .acid, and to afcer- 

 tain whether the fubftances which oppofe its preservation are 

 of fuch a nature as to be capable of being Separated by means 

 that depend lefs on the art of our laboratories. 



The lemon juice I employed had been clarified by filtra- 

 tion : and it had been kept for a year in a cellar, covered with 

 a little oil, according to the ufual method of the (hops. 



I. Spirit of wine mixed with this juice in a pretty large 

 quantity, did not render it turbid even after being kept 34 

 hours. 



Having evaporated about three pounds of it, in a gentle 

 heat, to the confiftence of fyrup, I obferved, as Scheele had 

 done, that the citric acid announced no difpofition to cryf- 

 tallize even when carried by evaporation nearly to the con- 

 fidence of extract. The reafon of this, no doubt, was, that 

 this acid, which is very cryftallizable, requires, however, but 

 little wate^ for its eryftallization. 



Lemon juice, by evaporation, afTumes the colour and dif- 

 agreeable odour of the extract: of plants; when rediffolved in 

 water, it reproduces a juice of a talle which full participates 

 of that of extracts. In a word, evaporation, which gives no 

 hope of the pofiibility of Separating the principles which alter 

 it, adds to it the inconvenience common to all extracts, which 

 is, that their folution in water never brings back the juice to 

 that tafte which it before had in the plants. 



DubuifTon, in a fupple'ment to his Art du Diftillateur, fays, 

 that the evaporation of lemon -juice in a gentle heat makes 



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