CLIII.—The dissociation pressures of alkali bicarbonates. Part I. Sodium hydrogen carbonate
Robert Martin Caven, Henry Julius Salomon Sand
Journal of the Chemical Society Transactions
IT is the object of the present investigation t o study the dissociation pressures of the various alkali bicarbonates in order to discover to what. extent the relative stability of each is connected with the basigenic behaviour of its metal, and the position of the latter in the periodic system. The equilibria which must be investigated for this purpose may be expressed by the equation: in which M indicates the atom of an alkali metal. This equation represents in its most general form a
... ponent equilibrium, but, as will be seen in the sequel, i t is sufficient for the purpose we have in vjew t o treat i t as one derived from the two components MHCO, and M,CO" whereby we limit ourselves to the case in which water and carbon dioxide occur in equimolecular proportions in the gaseous phase. Exact data connected with the subject are very scarce. I n 1835 Rose (Pogg. Ann., 1835, 34, 158) proved that solutions of sodium and potassium hydrogen carbonates may decompose at the ordinary temperature, yielding the normal carbonate and carbon dioxide, and the same conclusion has been arrived at in different ways by several other experimenters (Magnus, Pogg. Ann., 1837, 40, 590; Marchand, J . pr. Chem., 1845, 35, 389; Treadwell and Reuter, Zeitsch. anwg. Chem., 1898, 1 7 , 202). Corresponding results for solid sodium hydrogen carbonate were obtained by Gautier in 1876, when temperatures above 35O were employed (Ber., 1876, 9, 1434). I n connexion wifh his work on the solubilities of alkali bicarbonates, Dibbits, in 1874, determined approximately the partial pressure of carbon dioxide which was in equilibrium with saturated solutions of the respective salts at various temperatures ( J . pr. Chem., 1874, [ii], 10,440). Lescoeur, in 1-892, attempted t o measure the dissociation pressure of solid sodium hydrogen carbonate between 55O and looo, but does not appear to have obtained a true equilibrium, since the recorded results are very much lower than ours (AWL Chim. Phys., 1893, [vi], 28, 423). Lastly, McCoy, in 1903, carefully studied the equilibrium at 2 5 O between a solution containing sodium carbonate and sodium hydrogen carbonate and a gaseous phase composed of air, carbon dioxide, and water vapour (Amer. C h m . * Since these experiments were begun a very similar method for the measurement of vapour pressures htw been described by Johnston (Zeitsch. physiknl. Chem., 1908, 62, 333).