Chemistry of organic bodies. Vegetables / By Thomas Thomson.

  • Thomas Thomson
Date:
1838
Catalogue details

Licence: Public Domain Mark

Credit: Chemistry of organic bodies. Vegetables / By Thomas Thomson. Source: Wellcome Collection.

    40/1108 page 16
    atoms carbon and three atoms oxygen, yet as it is so easily formed by the action of nitric acid upon a variety of vegetable substances, we may, without any great breach of propriety, introduce it here in order to point out what happens when it is exposed to determinate degrees of heat. 1. It was observed by Dobereiner that when the crystals of oxalic ~ acid are heated in contact with sulphuric acid, they are resolved into equal volumes of carbonic acid and carbonic oxide. The water of the crystals in this case combines with the sulphuric acid, and the other constituents resolve themselves into the two gases just mentioned.* This experiment which has been frequently verified, demonstrates the composition of anhydrous oxalic acid. For 1 volume carbonic acid is : : ; C QO? 1 volume carbonic oxide is . i A CO Hence oxalic acid is . f ; C? O? 2. Gay-Lussac has made some important experiments on the de- composition of oxalic acid by the naked fire in a glass retort.T When the crystals are heated to 208° they fuse into a liquid. At 230° a gas is disengaged along with the vapour of water, and the quantity of this gas increases progressively in proportion as the temperature of the acid is elevated by the loss of its water of crys- tallization. Between 248° and 266° the disengagement was very rapid, and it continued till the complete decomposition of the acid with some variations of temperature, which were not exactly marked. If the heat be raised slowly, the whole acid is decomposed. The gas obtained is a mixture of 6 volumes carbonic acid, 5 volumes carbonic oxide. The water distilled over was acid, and owed its acidity to the pre- sence of a quantity of formic acid, formed during the decomposition of the oxalic acid. , Now it is easy from the known constitution of oxalic acid and formic acid to explain what happens during this decomposition. Let us suppose 12 atoms of oxalic acid crystals put into the retort, they are composed 12 atoms anhydrous oxalic acid, 36 atoms water, they yield 12 volumes carbonic acid . : : Cl? O74 10 volumes carbonic oxide , 3 Cle Ole G22 034 12 atoms of oxalic acid : : ; C4 O36 Excess . : - CG? Q? But an atom of formic acid is composed of C? H O08. Let us suppose that one of the 36 atoms of water is decomposed and enters into the composition of the formic acid. Water is com- * Schweigger’s Journal fiir Chemie und Physik, xxiii, 66. + Ann. de Chim. et de Phys, xlyi, 218. Sin ny
    digitised image 1
    digitised image 2
    digitised image 3