340 
MANUFACTURE OF TARTARIC ACID. 
decomposition of the neutral tartrate of potash solution of the 
succeeding operation ; whilst that portion of it which is not re- 
quired for that purpose, may be dried over the coke ovens herein- 
after mentioned, and sold as manure. The expense of chloride of 
calcium, formerly employed to effect the decomposition of the tar- 
trate of potash, is thus saved, and the decomposition quite as effec- 
tually accomplished. The filtered solution of tartaric acid is next 
concentrated by evaporation, and crystallized; for this purpose it 
is placed in wooden vessels lined w 7 ithlead, of various lengths and 
widths, and about nine inches deep, along which coils of lead-pipe 
are made to traverse ; steam is then passed through these pipes, 
and the concentration of the acid is thus effected. Deposits of 
sulphate of lime, held in solution by the acid, take place around 
the lead pipes during the process of concentration. As the solu- 
tion of tartaric acid is readily decomposed, care should be taken 
that the temperature does not much exceed 165° Fahr. There can 
be no doubt that the adoption of the vacuum-pan would prove 
highly advantageous in the concentration of tartaric acid solutions. 
The plan of pumping cold air into the tartaric acid solution whilst 
undergoing concentration, has been tried on a large scale, but ex- 
perience having proved that a loss of acid resulted, the process has 
been abandoned. 
When the liquor has attained the specific gravity of about 
1500° it is drawn off into suitable crystallizing vessels; these 
are formed of sheet-lead, are cylindrical in shape, usually about 
four feet in heighth, and two feet in diameter, and each capable 
of holding about five cwt. of tartaric acid in solution ; these 
crystallizers are placed in a warm situation, and in the course of 
three or four days there is produced in each a crop of crystals 
averaging about two cwt. These crystals, however, contain a por- 
tion of coloring matter, which is removed by placing them in a 
vessel lined with lead, with water and animal charcoal (previously 
well washed with dilute hydrochloric acid to remove the calcareous 
salts contained in it,) steam is blown in, the acid is dissolved, 
and the saturated solution digested with the animal char- 
coal, filtered, again concentrated, and crystallized. The crys- 
tals are next washed, drained, and lastly, dried on wooden 
trays lined with thin sheet-lead, placed in a room heated by steam. 
