82 Dr, Odling, 07t Magnesium, Calcium, [March 11, 



which is much more expensive, sodium is the most basylous of the 

 metals; it even serves to displace the quasi-metallic grouping of 

 hydrogen and nitrogen, known as ammonium. Amalgam of sodium, 

 introduced into a solution of chloride of ammonium, forms chloride of 

 sodium and amalgam of ammonium. But these most highly basylous 

 metals, potassium and sodium, afford remarkable exceptions to the law 

 that basylous metals replace less basylous metals. Thus, althougii 

 when sodium is heated with hydrate of iron, the sodium expels the iron, 

 as might be anticipated, yet when hydrate of sodium and iron borings 

 are heated together, a reverse action takes place, and the iron turns 

 out the sodium, as in Gay-Lussac's process for the production of that 

 metal. This reciprocity of results is only an extreme instance of a 

 tolerably general law. In a similar manner, though mercury displaces 

 silver from argentic nitrate, yet silver displaces mercury from mercu- 

 rous nitrate. Though copper displaces silver from argentic sulphate, 

 yet silver displaces copper from cupric sulphate. Though cadmium 

 displaces copper from cupric chloride, yet copper displaces cadmium from 

 cadmic chloride, &c. &c. Some of these results appear to depend on 

 Brodie's law of homogeneous affinity : thus, when cadmium is deposited 

 upon copper, we have the reaction, 



+ - +- +- +- 



Cu Cu + Cd CI = Cd Cu + Cu CI 



y. Reduction by charcoal. — This is the most usual means adopted 

 for the production of metals on a manufacturing scale. Brunner*s 

 process for obtaining potassium and sodium is an exact counterpart of 

 the commercial process for obtaining zinc ; in each case the metal is 

 evolved in the gaseous state, or distilled, from a heated mixture of its 

 carbonate with charcoal. The same reciprocity exists between sodium 

 and charcoal as between sodium and iron. Thus carbon decomposes 

 oxide and carbonate of sodium to form carbonic oxide or anhydride 

 (acid). But sodium heated in carbonic oxide or anhydride liberates 

 carbon, and forms oxide or carbonate of sodium. Indeed chemical 

 re-actions are not absolute but conditional ; under reversed condition 

 we obtain reversed results. 



Magnesium. — Chloride of magnesium is the source from which the 

 metal is usually obtained. Becquerel succeeded in procuring octahedral 

 crystals of magnesium by the electrolysis of a solution of chloride of 

 magnesium. But the metal is preferably obtained by electrolysing the 

 fused salt. Matthiessen employs a common tobacco-pipe for the 

 purpose : the bowl is filled with fused chloride of magnesium, or rather 

 with a mixture of chloride of magnesium and chloride of potassium, 

 which is more easily prepared than the pure salt. The negative pole, 

 to which the magnesium attaches itself, consists of an iron wire passing 

 through the pipe-stem. The positive pole consists of a pointed piece 

 of gas-carbon dipping into the fused mixture of salts. Magnesium is 

 however obtained most abundantly by heating its chloride with me- 

 tallic sodium, as before referred to. The sodium turns out the mag- 



