246 VINEGAR, CIDER, AND FRUIT-WINES. 



under the second boiler is closed by a register, and the con- 

 tents of the boiler being emptied into a large iron trough, 

 the boiler is at once refilled with a new mixture of Glauber's 

 salt and milk of lime, while a fresh portion of wood-vinegar 

 is brought into the first boiler, etc. 



In the trough an abundant precipitate is formed from which 

 the fluid is drawn off by means of several cocks placed at dif- 

 ferent heights. The wash-waters serve for mixing fresh quanti- 

 ties of Glauber's salt and lime. The solution of sodium acetate 

 is evaporated, and further worked, as given under a. 



This method is, however, inferior to the one described under 

 , because much fuel is required for the complete distilling over 

 of the wood-vinegar, which is not the case in a, and further be- 

 cause the substitution between Glauber's salt and calcium acetate 

 is not as smooth as above supposed for the sake of simplicity/ the 

 precipitate consisting not only of gypsum, but of a double salt of 

 gypsum and sodium sulphate which dissolves with difficulty. 

 The actual process is expressed by the equation : 



2(Xa 2 So 4 ) + (C 2 H 3 2 ) 2 Ca - 2(C 2 H 3 O 2 Xa) + 

 Na,Ca(S0 4 ) 2 , 



which shows that only half of the sodium contained in the Glau- 

 ber's salt is converted into acetate, the other half being lost. 

 Moreover, there is a large quantity of insoluble precipitate which 

 has to be thoroughly washed in order to avoid considerable 

 loss ; and, finally, the solution of the acetate constantly deposits 

 gypsum during evaporation, necessitating cleansing of the pans. 



The mother-lye from which the sodium acetate has crystallized 

 out contains a considerable quantity of the latter. It is therefore 

 again evaporated to 27 B. and on cooling yields crystals. By 

 repeating this concentrating and cooling finally nothing more crys- 

 tallizes out, the whole forming a crystalline mass, which, by absorp- 

 tion of water from the air, becomes semi-fluid, and consists of very 

 little sodium acetate mixed with the sodium salts of the other 

 fatty acids previously mentioned. 



Barre, in 1869, showed that besides acetic acid the following 

 acids occur in wood-vinegar : formic acid, CH 2 O 2 , propionic acid, 



