[31] The molecule of metallic potassium (Scott, 1887), like that of mercury, contains only one atom, and it is probably in virtue of this that the molecules CO and K combine together. But as in the majority of cases potassium acts as a univalent radicle, the polymeride K2C2O2 is formed, and probably K10C10O10, because products containing C10 are formed by the action of hydrochloric acid. The black mass formed by the combination of carbonic oxide with potassium explodes with great ease, and oxidises in the air. Although Brodie, Lerch, and Joannis (who obtained it in 1873 in a colourless form by means of NH3K, described in Chapter VI., Note [14]) have greatly extended our knowledge of this compound, much still remains unexplained. It probably exists in various polymeric and isomeric forms, having the composition (KCO)n and (NaCO)n.
[32] The connection of the cyanogen compounds with the rest of the hydrocarbons by means of carboxyl was enunciated by me, about the year 1860, at the first Annual Meeting of the Russian Naturalists.
[33] Thus, for instance, oxamide, or the amide of oxalic acid, (CNH2O)2, is obtained in the form of an insoluble precipitate on adding a solution of ammonia to an alcoholic solution of ethyl oxalate, (CO2C2H5)2, which is formed by the action of oxalic acid on alcohol: (CHO2)2 + 2(C2H5)OH = 2HOH + (CO2C2H5)2. As the nearest derivatives of ammonia, the amides treated with alkalis yield ammonia and form the salt of the acid. The nitriles do not, however, give similar reactions so readily. The majority of amides corresponding to acids have a composition RNH2, and therefore recombine with water with great ease even when simply boiled with it, and with still greater facility in presence of acids or alkalis. Under the action of alkalis the amides naturally give off ammonia, through the combination of water with the amide, when a salt of the acid from which the amide was derived is formed: RNH2 + KHO = RKO + NH3.
The same reaction takes place with acids, only an ammoniacal salt of the acid is of course formed whilst the acid held in the amide is liberated: RNH2 + HCl + H2O = RHO + NH4Cl.
Thus in the majority of cases amides easily pass into ammoniacal salts, but they differ essentially from them. No ammoniacal salt sublimes or volatilises unchanged, and generally when heated it gives off water and yields an amide, whilst many amides volatilise without alteration and frequently are volatile crystalline substances which may be easily sublimed. Such, for instance, are the amides of benzoic, formic, and many other organic acids.
[34] The acid salt, (NH4)HCO3, on losing water ought to form the carbamic acid, OH(CNH2O); but it is not formed, which is accounted for by the instability of the acid salt itself. Carbonic anhydride is given off and ammonia is produced, which gives ammonium carbamate.
[35] In the normal salt, 2NH3 + CO2 + H2O, in the acid salt, NH3 + CO2 + H2O, but in the commercial salt only 2H2O to 3CO2.
[36] Naumann determined the following dissociation tensions of the vapour of ammonium carbamate (in millimetres of mercury):—
| -10° | 0° | +10° | 20° | 30° | 40° | 50° | 60° |
| 5 | 12 | 30 | 62 | 124 | 248 | 470 | 770 |
Horstmann and Isambert studied the tensions corresponding to excess of NH3 or CO2, and found, as might have been expected, that with such excess the mass of the salt formed (in a solid state) increases and the decomposition (transition into vapour) decreases.