MANUFACTURE OF WOOD-VINEGAR. 



245 



Fig. 59. 



through which the mother-lye drains off. The crystals are finally 

 washed Avith a saturated solution of pure salt and passed through 

 a centrifugal. The salt thus obtained 

 is entirely pure ; but its preparation 

 requires very careful and skilled work- 

 men. 



b. Since the reduction in the price 

 of soda the method of saturation de- 

 scribed under a has been generally 

 introduced. Formerly the sodium 

 acetate was prepared by means of 

 Glauber's salt (sodium sulphate) and 

 lime. Notwithstanding its many de- 

 fects, this method, which was introduced by Mollerat, is still in use 

 in some factories. 



The wood-vinegar is saturated with slaked lime and the 

 calcium salt decomposed with Glauber's salt ; gypsum (calcium 

 sulphate) is precipitated while sodium acetate remains in solu- 

 tion. Or, a mixture of Glauber's salt and lime (for 5 parts 

 of crystallized Glauber's salt 1 part of burnt lime) is employed 

 for saturation and constantly stirred while the wood- vinegar is 

 added. 



Crude wood- vinegar can be used instead of the product freed 

 from wood-spirit, the distilling off of the wood-spirit and acetone, 

 together with the saturation, being executed in one operation, as 

 follows : 



The crude wood-vinegar is distilled in a large copper boiler hold- 

 ing about 106 cubic feet over an open fire or by means of steam. 

 The vapors pass through a pipe into a similar boiler which is 

 heated by the heat escaping from the first. In this boiler the 

 mixture of Glauber's salt and milk of lime is kept in constant 

 agitation by a stirring apparatus making about 25 revolutions 

 per minute. The wood-spirit, etc., which is not fixed in the 

 second boiler, passes into the condensing apparatus. 



In order to see whether the point of saturation is reached, 

 samples are from time to time taken by means of a stop-cock 

 on the bottom of the second boiler ; litmus paper being first col- 

 ored blue and finally red. When this is the case, the flue 



