ACETIC ACID. The sour principle of vinegar. This acid occurs in the vege table kingdom in the elder and some varieties of Aim. It exists in the gas tric juice and other animal secretions. When vegetable matter is distilled in close vessels, this acid is always one of the products. Alcoholic liquids are ca pable of producing acetic acid, and it is the last stage in the fermentation of many vegetable bodies containing starch or su gar—as paste, &c. Pyroligneous acid is acetic acid derived from wood—for the manufacture of which see under that head. The purest acetic acid is that made by the oxydation of alcohol. The oxydation is produced by the action of the atmosphere. In Germany, where this process was first adopted, the alco hol was exposed in very large surface to the action by being made to trickle along the shavings of wood. These were placed in a deep barrel, perforated at the sides with a number of holes so that free access of air to the inside of the vessel was effected ; on the upper part of the barrel was a raised rim capable of hold ing a certain head of alcohol, and the up per end of the barrel was perforated with a few fine apertures so that the alcohol might slowly stream down on the shav ings ; it was thus exposed to a large quantity of air constantly renewed, and by the time it reached the bottom of the vessel it was converted into vinegar, or dilute acetic acid. It was drawn off by a cork from the lower part of the barrel, placed in a still and distilled with a gen tle heat ; the portions which come over first, contain the acetic acid.
A great improvement on this process has been the substitution of spongy pla tinum cre PLATINITIA) for the wood shav ings. he principle in both is the same, being the oxydation of alcohol by the air. Into a large case of wood with glass sides or windows for observing the process, and fitted with shelves within a few inches of each other, is placed a number of saucers filled with the alco hol, and over each saucer is suspended a small portion of the black platinum powder. The quantity of alcohol in the
saucers varies with the dimensions of the case ; 100 cubic inches of air being capable of oxydizing 11 grains of abso lute alcohol, and converting it into 12'2 of absolute acetic 'acid and 61 grains of water. The case must now be warm ed up to 80° Fahr. by solar or arti ficial heat and the alcohol induced to evaporate off the saucers by some lead ing points, as strings or folds of paper set endways in the liquid : in a short time the temperature inside the box rises ; vapors form, condense on the in side, and roll down to the bottom. This process continues so long as there is any oxygen of the air in the vessel uncon sumed : now and then fresh supplies of air are needed-8 oz. of the platinum powder will in a day's work convert one pound of alcohol into acetic acid. The change arises from the absorption of oxy gen from the air, and its union with the elements of alcohol, which results in the formation of acetic acid and water. By the chemist the change is expressed by the formula : alcohol from air Its acetic acid + 3 II 0 wa ter. Hence 100 parts of alcohol absorb nearly 69 parts of oxygen, and there are produced nearly 111 parts of acetic acid and 58 parts of water. Strong acetic acid is also made by distilling crystalled bin acetate copper (verdigris) in close ves sels at a high heat. It can also be made by distilling acetate of potass and acetate of lead (sugar of lead) with oil of vitriol. In its purest state it is united with an atom of water, and has a specific gravity of 1'063. It is caustic on the tongue and to the skin : it is used as a scent, and when essential oils are added, constitutes the aromatic vinegar. It dissolves cam phor, gluten, resins, gum resins, fibrine, and albumen.