220
ELEMENTS OF MATERIA MEDIC.A.
when collected and dried, resembles gum, and is destitute of nitrogen.During these changes we observe mouldiness ( Mucor mucedo) on its sur-face. Vinegar nourishes some microscopic animals, commonly thoughvery improperly termed eels (Vibrio Aceti). These may be destroyed bysubmitting the vinegar to heat. It is also infested by a small fly ( MuscaCellaris ).
( d .) Constituents of Vinegar. —Malt vinegar consists of water, aceticacid, colouring matter, a peculiar organic matter commonly termed mu-cilage, a small portion of alcohol, and a peculiar odorous principle. Vine-gar makers are allowed to add one one-thousand part by weight of sul-phuric acid. The strongest malt vinegar, called proof vinegar, (orNo. 24 vinegar) should contain 5 per cent, of real acetic acid ; but,according to Mr. Phillips, that of commerce does not usually con-tain more than 4’6 per cent. One fluidounce, or 446 grains of vine-gar of the latter strength, should saturate very nearly 58 grains ofcrystallized carbonate of soda, or dissolve about 20 grains of purewhite marble (carbonate of lime). In the Pharmacopoeia we are told,that a fluidounce of vinegar is saturated by 60 grains of crystallizedcarbonate of soda, two grains being allowed for saturating the sulphuricacid permitted to be added by law, and for decomposing the sulphatescontained in the water employed in vinegar-making (Phillips’s Translationof the London Pharmacopoeia). The quantity of sulphate of barytathrown down by the addition of solution of chloride of barium to a fluidounce of vinegar, should not exceed 1T4 grains (Phillips.) If the vinegarbe free from copper, lead, and other metallic matter, it forms no precipitateon the addition of hydrosulphuric acid.
(e.) Distillation of Vinegar. —In the Pharmacopoeia this is ordered tobe effected in a glass apparatus. The seven-eighths first distilled are tobe kept for use: they constitute the acetum distillatum of the LondonPharmacopoeia. If a copper still or pewter worm be employed, thedistilled product has a metallic impregnation. On the large scale,earthenware or silver condensing tubes are employed.
2. By the destructive Distillation of Wood . —This acidis procured by the distillation of wood in cast-iron cylinders. Oak, ash,birch, and beech woods, are employed: fir wood does not answer. Thebrushwood or spray of trees is sometimes used. The products are char-coal, which remains in the still, and various volatile substances; somecondensible, others not.
The condensation of the vapours is effected by passing them througha worm, kept cool by immersion in water. The condensible productsare water, acetic acid, and tar: these form crude pyroligneous acid.The incondensible products are carbonic acid and some inflammablegases: viz. carbonic oxide, light carburetted hydrogen, and olefiant gas.These are allowed to escape, or are burned in the furnace.