290 VINEGAR, CIDER, AND FRUIT-WINES. 



collected lead solution, which is effected (with the use of acetic 

 acid) when it shows a specific gravity of at least 36 B. The 

 solution being, however, basic, it is acidulated with strong acetic 

 acid and brought into the crystallizing vessels. 



This method is decidedly the best, because the evaporation" of 

 the solution is entirely or almost entirely omitted and the air of 

 the workroom is not contaminated by particles of sugar of lead, 

 which is very injurious to the health of the workmen. Further- 

 more, this method does not require the use of pure acetic acid, 

 since the impurities remain in the still. This, however, holds 

 good only for non-volatile impurities. For the production of 

 colorless salt, the crude acetic acid from wood-vinegar must 

 necessarily be purified, as above mentioned, by potassium chro- 

 matc and sulphuric acid. 



The crystallizing pans are either of stone- ware or of wood 

 lined with lead or thin copper, to which is soldered a strip of lead 

 down the sides and across the bottom, with the idea of rendering 

 the metal more electro-negative so as to prevent the acetic acid 

 from acting on it. The wooden crystallizing pans are about 4 

 feet long by 2 feet wide and from 6 to 8 inches deep, sloping 

 inwards at the edges. Shallow, slightly conical copper vessels 6 

 inches deep with a diameter of 29 J inches at the bottom and 31 J 

 inches at the top are also used. The stone- ware pans are placed 

 upon a slightly inclined level covered with lead. In these small 

 pans crystallization is complete in 24 hours, while from 48 to 72 

 hours are required with the use of the larger wooden vessels. 

 Crystallization being complete, the mother-lye is removed and 

 the vessels placed upon a wooden frame over a gutter of sheet- 

 lead to drain off, as. shown in Figs. 64 and 65. 



If especially beautiful crystals are to be obtained, the first 

 crystals, which are not very distinct, are again dissolved in 

 the water obtained by the condensation of the vapors escaping 

 from the still. The solution being evaporated to the proper 

 density is again allowed to crystallize. The crystals after suffi- 

 cient draining are placed upon linen spread over wooden hurdles 

 and dried at a moderate heat, not exceeding 75 F. In some 

 factories the heated air of a stove, placed outside the drying 

 house, is conveyed through pipes passing round the interior ; at 



