In the small holes are suspended pieces of thread or string, kept in their plaoe by knots at the upper end. In the larger holes aro fitted short glass or wooden tubes which go through the cover and servo as vents. About 18 in, from the bottom of the generator is fixed a second per forated shelf or false bottom, and some few indite above this the sides of the tub aro pierced with holds 11 in. in diameter which admit the necessary supply of air. Below the false bottom is an exit pipe for the liquid, preferably curving upwards when it reaches the outside until close upon the level of Ihe air-holes. Finally, the generator is filled from the false bottom to within short distance of the top shelf with shavings, chips of beech wood, or charcoal. The latter is preferable, as presenting a greater surface for oxidation than any other substance, but it requires frequent renewal,—not admitting of being cleansed. If shavings or chips are employed, they should be boiled in water and dried in a close oven before being used. Before passing the ulcoholie liquors into the generator, the shavings, and the vessel itself, are " soured" with hot strong vinegar to aceelerato the subsequent oxidation. The alcoholic liquors, usually consisting of 50 gallons of brandy of 60 por eent and 37 gallons of beer with about of ferment, are now introduced into the generator through a funnel in the cover shown at A, Fig. 4. The liquors percolate slowly through the shavings, chips, or charcoal, meet an ascending current of air, and undergo oxidation. Flowing over through tho exit siphon they are returned once more to Movers° the generator, or aro transferred to a second similar apparatus,—the latter being the preferable plan. By this
"quick" process, practised largely in Germany, France, and England, as much es 150 gallons of vinegar can be manufactured per diem in 10 tuns of the description shown in the drawing. The liquors should be as clear as possible—free from suspended organic substances—or else the chips or shavings become rapidly choked, and unless these are eonstantly cleaned by boiling in water, or renewed, equal distribution of the liquors is impossible. No pyroligneous acid, with admixture of tarry matters and oils, should be present, as they prevent oxidation.
The nitrogenous organic substances having promoted the acetification of the alcohol, settle out and then assume a new form ; they are known as " mother of vinegar." Treated with potash this " mother," a white gelatinous mass, loses its nitrogen, pure cellulose being left.
Further details of the process, and modifications of it--such as Ham's—concern rather the manufacturer of vinegar than of acetic acid, and these, together with further details relating to acetone fermentation, will be dealt with at length in a separate article upon vinegar.
It should be noted that simple oxidation of alcohol—by the carefully regulated action of air or an oxidizing agent—produces pure acetic acid, but in the ordinary acet,ous fermentation, where certain vegetable bodies are present, the acid is yielded in the form of rincwur by admixture with various organic) impurities.