xx DISSOCIATION 533 



are not shown in the ordinary equations. The metals potass- 

 ium, sodium, magnesium, zinc, cadmium and iron do not 

 dissolve in liquefied hydrogen chloride, nor does it act at all 

 on quicklime or marble (Gore, Proc. Roy. Soc.> 1865, 14, 204- 

 213). Dry chlorine does not act upon sodium either at the 

 ordinary temperature or when fused (Wanklyn, Chem. News, 

 1869, 20, 271), and has but little action on silver, zinc, magne- 

 sium and potassium (Cowper, Trans. Chem. Soc., 1883, 43, 

 153-155). Nitric acid, which has been freed from water and 

 from lower oxides of nitrogen, has no action upon purified 

 copper, silver, cadmium or mercury, nor upon commercial 

 magnesium at ordinary temperatures ; even when boiling it 

 does not attack iron or tin, nor dissolve Iceland spar or marble 

 (Veley, Phil. Tra/is.,i8^S, A. 191, 388). Copper does not 

 dissolve readily even in diluted nitric acid if freed from 

 lower oxides of nitrogen, but as soon as it begins to dissolve 

 these are produced in increasing quantities and the action 

 is rapidly accelerated (Veley, Proc. Roy. Soc.^ 1889, 46, 216- 

 222). Highly purified zinc, redistilled in a vacuum, is 

 "nearly unacted on by sulphuric or hydrochloric acid" 

 (Reynolds and Ramsay, Trans. Chem. Soc., 1887, 51, 857), 

 but it is rendered soluble by contact with the less active 

 metals, such as lead, copper and platinum. Metals do not 

 combine with dried chlorine, nor sodium and potassium 

 with dried oxygen ; dry lime does not combine with carbonic 

 anhydride (Veley, Trans. Chem. Soc., 1893, 63, 821), nor 

 does sulphuric anhydride combine with dry quicklime or 

 with the dry oxide of copper (Baker, Trans. Chem. Soc., 

 1894, 65, 622). Pure iron does not rust, does not dissolve 

 in cold dilute sulphuric or nitric acid, and has no action 

 on aqueous copper sulphate or copper nitrate (Lambert, 

 Trans. Chem. Soc., 1912, 101, 2069). 



In the case of metals dissolving in acids, the conditions 

 for dissolution are clearly identical with those for the pro- 

 duction of a battery, namely, two electrodes (e.g. zinc and 



