Volume 1

A dictionary of chemistry and mineralogy, with an account of the processes employed in many of the most important chemical manufactures. To which are added a description of chemical apparatus, and various useful tables of weights and measures, chemical instruments, &c. &c / by A. & C.R. Aikin.

  • Aikin, Arthur, 1773-1854.
Date:
1807
Catalogue details

Licence: Public Domain Mark

Credit: A dictionary of chemistry and mineralogy, with an account of the processes employed in many of the most important chemical manufactures. To which are added a description of chemical apparatus, and various useful tables of weights and measures, chemical instruments, &c. &c / by A. & C.R. Aikin. Source: Wellcome Collection.

    14/768 (page 2)
    than the acetous, holding in folution a certain quantity of empyreumatic oil. Laftly, the action of the ftronger mineral acids upon the fame vegetable and animal mat- ters, tends to the production of the acetous acid, which is molt ftrikingly illuftrated by the final converfion into vinegar of all the inter- mediate and native vegetable acids, the malic, tartareous, gallic, oxalic, &c. The experiments that prove this interefting fad we fhall prefently relate. Pure acetous acid is conveniently procured from common vinegar by diftillation. The latter contains, befides acetous acid, a confiderable quantity of foreign ingredients, fuch as alcohol, and particularly tartar, and the extradive mu- cilage, which gives it its red or yellow colour, and caufes it to mould and lofe its acid when long kept expofed to warm air. Of thefe the alcohol, the water, and the pure acetous acid, are the only volatile ingredients, and therefore feparable by diftillation. The diftillation of vinegar is carried on in the large way by the druggifts, for general purpofes, and for the preparation of fugar of lead 5 in fome parts of the fouth of Prance for the preparation of verdigris ;c with thefe it is dif- tilled in a tinned copper veflel, as the adion of vinegar upon tin is but flight. For the labora- tory, however, glafs veflels fhould be employed, or if the retort or boiler be of metal, the head or receiver fhould be of glafs or earth. The ftrongeft common vinegar is to be put into a glafs retort with a receiver, and brought to boil on a fand bath. A watery and flightly acid vapour firft condenfes, which is a very weak acetous acid, and may be fet afide. Then the cliftilled liquor (ftill continuing equally clear and colourlefs, but a little empyreumatic in fmell and tafte) becomes more ftrongly acid, and continues fo to the laft. This is the common acetous acid or diftilled vinegar. Towards the end of the procefs, the refidue is very apt to acquire and communicate a burnt fmell and tafte: this is prevented by carefully regulating the fire, and, if it be worth while, by adding to the liquor in the retort a little warm water; but when about five-fixths of it is diftilled, the procefs fhould be difcontinued. The refidue is very four, of a muddy brown red, and a ftrong pungent burnt fmell. It contains, befides the remaining acetous acid, fome tartar, and tar- tareous acid, and a flimy vegeto-animal matter, which has not been perfectly analyfed. By further evaporation it becomes thick, tenacious, and at laft a folk! blackilh extract. On urging the fire to deftru£live diftillation, it gives a four empyreumatic inflammable vapour, an empy- reumatic oil, and ammonia. The coal contains potafh, mixed with a fubftance which gives oxalic acid in cryftals when boiled with the nitric acid.d The vapour of heated vinegar, or the acetous acid gas, as it has been termed, is inflammable. The truly acid part of the purified acid is ftiil mixed with a large portion of water. Means have been devifed for eondenfing or concen- trating the acid in a fmaller bulk. Diftillation alone, as we have feen, is not competent to this purpofe; for, though fome of the water riles nearly pure juft at firft, yet it foon becomes very four, as the acid is almoft equally volatile by heat as water. The effedl of froft in concentrating vinegar is very ftriking. If a quantity of this acid, dif- tilled or not, be fet out in the air in winter, when the cold is below about 26° a tender flaky ice forms in the liquor, and renders a large portion of it folid; on breaking it, a portion, ftill fluid, is found beneath, which is to be care- fully drained off from the ice. This fluid is the acetous acid, concentrated by the lofs of all the frozen part, which laft is taftelefs or very nearly fo, and is little elfe than pure water. A further expofure of the ftrong acid to a fharper cold, will produce a fimilar and en- creafed condenfation, till at laft the procefs mult be flopped, either on account of the cold not being now fufficient to feparate the water from the conftantly ftrengthening acid, or from the ice itfelf becoming acid. Diftilled vinegar may be brought by this mode of concentration from the common fpecific gravity of 1.006 to that of 1.029.' this ftate ^ ftifi retains the phyfica! properties of the watery acid, but in a much more exalted degree; its fmell is ftrongly and agreeably pungent; its tafte fharp, almoft to caufticity ; and as a chemical agent, it is much more a£live and powerful in every refpe£t. Common vinegar is equally ftrengthened by freezing, but as the colouring matter chiefly remains in the unfrozen part, it becomes more highly tinged as the more condenfed. A more eflfettual mode of concentrating this acid is by previous union with an alkali, an earth, or a metallic oxyd, and bringing it by evaporation to a folid confiftence. In fo doing, all the fuperfluous water of the acid is feparated, and if the acid be afterwards expelled from the fait by means of a ftronger affinity, it appears in the moft concentrated form of which it i* c Chaptal, * Cren. (Syftem.Handbuch.) * Owe Expcr.