MANUFACTURE OF TARTARIC ACID. 
339 
in motion ; the result is, that the free tartaric acid contained in 
the bitaitrate of potash unites with the base of the whiting, form- 
ing insoluble tartrate of lime, which precipitates to the bottom of 
the generator, leaving the neutral tartrate of potash in solution, the 
carbonic acid having escaped through the exit-pipe in the gase- 
ous form. 
Having thus removed one equivalent of tartaric acid from its 
combination with potash, the next part of the process is to remove 
the other; and this is effected by the addition of sulphate of lime 
in the state of paste, to the solution of tartrate of potash ; heat 
and agitation are again applied, the tartrate of potash is decom- 
posed, the second equivalent of tartaric acid enters into combina- 
tion with the base of the sulphate of lime, and tartrate of lime 
precipitates to the bottom to join that formed in the previous ope- 
ration, whilst the potash united with sulphuric acid remains in 
solution as sulphate of potash. The solution of sulphate of potash 
thus formed, is drawn off when clear, into suitable reservoirs to 
be treated, as hereinafter described. The tartrate of lime is 
next well washed with two or more successive charges of cold 
water ; these washings contain more or less of sulphate of potash, 
and are run off into suitable reservoirs. To the remaining tartrate 
of lime a sufficient quantity of water is then added, together with 
the requisite quantity of sulphuric acid, to effect its decomposition ; 
sulphate of lime is precipitated, and tartaric acid remains in solu- 
tion. The whole contents of the generator are now run off into 
a wooden back lined with lead, some fifteen or sixteen feet in length, 
six in width, and two in depth, furnished with a perforated 
false bottom, and lined throughout with stout twilled flannel. This 
back serves as a filter, and the filtered solution of tartaric acid 
passes off through a pipe, connected with the bottom of the back, 
into suitable reservoirs. When the acid solution has passed 
through the filter, water is carefully added to the sulphate of lime 
remaining, in such a way as to insure its uniform percolation 
through the mass, and not to run off through partial channels or 
fissures formed in the sulphate, which would prevent the entire re- 
moval of the acid. As soon as the residuary sulphate of lime is 
quite tasteless, and the filtered liquor free from tartaric acid, the 
pasty mass of sulphate of lime is removed by means of wooden 
shovels, and as much of it as may be required is again used in the 
