MANUFACTURE OF CITEIC ACID. 
345 
Manufacture of Rochelle Salt. — This double tartrate of soda 
and potash is prepared in the same apparatus as that described in 
the manufacture of tartaric acid. A solution of crystals of soda 
is first made, and to it is gradually added the bitartrate of potash 
in the form of crude tartar, the free tartaric acid in the bitartrate 
combines with the soda, carbonic acid is evolved, and the resulting 
solution is composed of one equivalent of neutral tartrate of soda 
and one of neutral tartrate of potash. This solution is drawn off, 
concentrated by evaporation, crystallized, the crystals re-dissolved 
and digested with animal charcoal, the solution filtered and re- 
crystallized ; the product obtained consists of colorless crystals of 
Rochelle salt. 
Manufacture of Citric Acid. — In the manufacture of citric acid 
the same apparatus is employed as we have described under tartaiic 
acid. Into the generator any given quantity of concentrated lime 
or lemon-juice, as imported from Sicily, is placed, and to it is added 
as much whiting as will suffice to neutralize the citric acid it con- 
tains ; carbonic acid gas is evolved, which may be applied to the 
manufacture of bicarbonate soda and carbonate of lime, as above 
mentioned, and citrate of lime is precipitated to the bottom of the 
generator. The supernatant liquor containing much of the extractive 
matter of the lime-juice is run off, and as much dilute sulphuric acid 
added to the sulphate of lime as will serve to liberate the citric acid 
it contains, whilst the sulphate of lime formed is precipitated. The 
mixture of citric acid and sulphate of lime is then run off to a 
filter back, arranged in the same way as that described in treating 
tartaric acid, and the operations of washing the residuary sulphate 
on the filter, concentrating the juice by evaporation, and subse- 
quent crystallization and purification, are all precisely similar to 
those described under tartaric acid. As citric acid is even more 
liable to decomposition than tartaric acid, still greater care must 
be taken in its concentration and subsequent treatment. Evapora- 
tion in vacuo is particularly desirable in the case of citric acid, and 
the centrifugal process of drying might also be employed with 
great advantage. — Pharmaceutical Journal and Transactions, 
February, 1851. 
