Organic chemistry / by W.H. Perkin and F. Stanley Kipping.

  • Perkin, W. H. (William Henry), 1860-1929
Date:
1905
Catalogue details

Licence: In copyright

Credit: Organic chemistry / by W.H. Perkin and F. Stanley Kipping. Source: Wellcome Collection.

    34/660 (page 14)
    the substance liquefies—that is to say, its melting-point (m.p.) *—is noted. QUALITATIVE ELEMENTARY ANALYSIS. A pure compound having been obtained, it is often possible, by noting its appearance, smell, crystalline form, solubility, and other properties, and by determining its melting- or boiling-point, to prove that it is identical with some substance the composition of which is known; f when, however, this cannot be done, the next step is to ascertain of what elements the substance is composed. In order, in the first place, to make sure that the substance contains carbon—that is to say, that it really is an organic compound—a small quantity is heated on platinum foil. If it inflames and burns away, or swells up, giving a black mass, which on strongly heating entirely disappears, the substance is in all probability organic. The metallic salts of organic acids usually char when treated in this way, and on further heating, the carbonaceous matter burns away, leaving a residue which may be dissolved in water or acids and examined by the usual methods of inorganic analysis. Sodium acetate, for example, leaves sodium carbonate; copper acetate, the oxide of the metal; and silver acetate, metallic silver. If a halogen, sulphur, or phosphorus be present in the acid, it is generally found in the residue in combination with the metal. The behaviour of a substance when heated with concentrated sulphuric acid often affords an indication of the presence of * The observed melting- or boiling-point of a substance is usually rather lower than the true value, because, as a rule, a portion of the column of mercury is not immersed in the heating liquid or vapour. f The identity of two solids is best tested by mixing a small quantity of the substance under examination with an appi'oximately equal quantity of the compound with which it is supposed to be identical, and then deter- mining the melting-point of the mixture; if it be the same as that of the separate constituents, the identity of the latter may be taken to be established.