98 VINEGAR, CIDER, AND FRUIT-WINES. 



Air-dried wood contains on an average 20 per cent, of water 

 and during acidulation this water must be gradually replaced by 

 vinegar ; hence the vinegar trickling from the generators will 

 remain poor in acetic acid and rich in water until the shavings 

 are entirely saturated with pure vinegar and the water is expelled. 



The removal of the water from the shavings and its substitu- 

 tion by vinegar are effected by osmose, i. e., the cells of the wood 

 surrounded by vinegar yield a fluid consisting of water and ex- 

 tractive substances of the wood and absorb sufficient of the 

 exterior fluid until both liquids have the same composition. Now, 

 by pouring only a small quantity of vinegar at one time over the 

 shavings in the generators, as is done in the acidulation according 

 to the old method, the course of the process is very slow, 14 days 

 or more, as already mentioned, being required before the vinegar 

 running off shows no longer a change in its concentration. 



In a generator in a stage of acidulation an uninterrupted 

 though slight current of air upwards takes place, since even 

 with the use of the best heating apparatus the air in the upper 

 layers is warmer than in the lower. This current of air- becomes 

 stronger with the development of larger quantities of vinegar 

 ferment and causes a large absolute loss of vinegar; the greater 

 portion of this loss must be set down as being due to evaporation, 

 which must be considerable on account of the great surface over 

 which the vinegar is distributed, and the smaller portion to con- 

 sumption by the vinegar ferment. 



By placing the shavings in vinegar the above-described process 

 of substitution of vinegar for the fluid contained in the cells of 

 the wood takes place very quickly, and, theoretically, it would 

 therefore seem to be advisable to follow the same course on a large 

 scale, i. e., to saturate the shavings with vinegar before placing 

 them in the generators. By using artificially dried shavings 

 (see p. 67) the saturation is effected in the course of a few hours, 

 the dry woody tissue absorbing the fluid like a sponge. 



The shavings, while still hot, are brought into a vat and covered 

 with the vinegar to be used for acidulation. In about 12 hours 

 they are thoroughly saturated ; the excess of vinegar is drawn off 

 through the tap-hole in the bottom of the vat, and having ab- 

 sorbed neither water nor extractive substances from the steamed 



