MANUFACTURE OF PARATARTARIC ACID. 
341 
By these means, a colorless acid of great purity is obtained, 
which is then packed in casks for sale. The mother-liquors of 
the first crystallization are again concentrated, and the crystals 
obtained, digested as before described with animal charcoal, until 
at last, by the accumulation of vegetable and other foreign mat- 
ters, the liquors are no longer crystallizable ; they are then decom- 
posed by means of chalk, and the tartrate of lime thus obtained 
added to the produce of a new operation. It is found in practice 
that a slight excess of sulphuric acid is necessary in order to 
obtain fine crystals of tartaric acid ; care, however, must be 
taken to guard against the accumulation of sulphuric acid in 
the process of manufacture, to the risk of destroying the tar- 
taric acid. 
With respect to the drying of this acid, there can be no doubt 
that the centrifugal method of drying would be far superior to the 
present mode, as the crystals often adhere to the lead-lining of the 
drying trays, and having to be forcibly detached, their shape and 
the general appearance of the acid becomes much impaired ; where- 
as, by the centrifugal mode of drying, the crystals may be obtained 
of a more perfect and regular shape, and the general appearance 
of the acid greatly improved. 
The principal consumers of tartaric acid are the calico-printers, 
who use it for the purpose of evolving chlorine from solution of 
chloride of lime, in the production of white, or what is technically 
termed discharged patterns upon a colored ground. Its pharma- 
ceutical uses are too well known to require comment. Tfu 
average annual quantity manufactured in Great Britain may be 
taken at about 1,000 tons, of which a certain quantity is exported 
to the continent of Europe and to the United States. 
Paratartaric Acid. — There is occasionally to be met with in the 
market, a tartar obtained from the grapes grown in the department 
of Vosges, which contains a large proportion of paratartaric or 
racemic acid. This acid may be distinguished from tartaric acid 
by its silky, needle-shaped crystals, and its insolubility compared 
with tartaric acid, 100 parts of water at 60° dissolving only 14.1 
racemic acid, whilst 100 parts of water at 60° dissolves 64.8 of 
tartaric acid. In the second volume of the Records of General 
Science, will be found a series of papers on this acid and its 
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