264 VINEGAR, CIDER, AND FRUIT-WINES. 



bottom from being obstructed by the sulphate crystallizing out, 

 sufficient pure acetic acid is previously poured into the vat to 

 cover the perforated bottom. By opening the stop-cock the 

 acetic acid runs off, which, however, contains a small quantity of 



Fig. 62. 



sodium sulphate in solution. The remaining sulphate is washed 

 with water, and, after mixing the latter with the acid, the mixture 

 is brought into stoneware-pots which are placed in cold water for 

 about 8 days, whereby the greater portion of the sodium sulphate 

 is crystallized out. The very small quantity remaining imparts, 

 however, a laxative quality to the salt, and hence must be con- 

 verted into a salt which does not possess this medicinal property. 

 This is effected by mixing the acid siphoned off in a vat with 

 pure calcium acetate, the required quantity of which has to be 

 determined by a test on a small scale. The gypsum formed 

 gradually settles to the bottom, while a corresponding quantity 

 of newly-formed sodium acetate remains dissolved in the acid, 

 which is, however, not injurious. 



The process may also be executed by bringing 100 pounds of 

 the salt in very small crystals or finely pulverized into a stone- 

 ware vessel, and adding at one time 35 or at the utmost 35.5 

 pounds of concentrated sulphuric acid in such a manner that it 

 lies on the bottom of the vessel below the salt. Mixing is then 

 gradually effected so as to avoid heating as much as possible. 



