1859.] Lithium J and their Congeners. 83 



nesium, which collects in globules that may be melted together under a 

 flux of low density. Magnesium is a solid metal of a silver-white colour. 

 Its appearance contrasts favourably with that of aluminium, which has 

 a decided bluish tinge. The freshly cut surface of metal is highly lus- 

 trous ; it does not tarnish in dry air, and acquires only a film of oxide 

 in moist air. Magnesium is but very slowly acted upon by pure cold 

 water. It decomposes boiling water somewhat rapidly with evolution 

 of hydrogen. Its specific gravity is 1 • 75. It is about one and a half 

 times lighter than aluminium, and is indeed the lightest of all metals 

 that are permanent in the air. One cubic inch of platinum balances 

 124 cubic inchesof magnesium, and only 8J cubic inches of aluminium. 

 At ordinary temperatures magnesium is somewhat brittle, and may be 

 readily cut or filed. It is neither very malleable nor very ductile ; 

 but, at an increased temperature, may be hammered into plates, and 

 drawn or rather pressed into wire by Matthiessen's process. The 

 metal is placed in a small hollow steel cylinder, having a hole drilled 

 in its anterior face. Through this hole the metal is forced in the form 

 of wire, by means of a press, acting through the intervention of an 

 iron piston, fitting into the hollow of the cylinder. Magnesium is 

 readily volatile ; so much so indeed, as to allow of its being purified 

 by distillation in an atmosphere of hydrogen. It is a highly com- 

 bustible metal, and burns brilliantly in air or oxygen, with a pure* 

 white flame. A magnesium wire, ignited at one end, will continue to 

 burn through its entire length. Magnesium corresponds closely in its 

 properties with zinc, and through zinc approximates to cadmium. The 

 atomic weight of zinc is the mean of the atomic weights of magnesium 

 and cadmium ; and the atomic volume of zinc is the mean of the 

 atomic volumes of magnesium and cadmium. 



Calcium, — This metal does not result from the action of sodium 

 upon chloride of calcium, but is obtainable only by the electrolysis of 

 that salt, rendered a conductor by fusion. It is a solid metal, of a 

 somewhat yellowish colour. It is highly lustrous, but tarnishes quickly 

 in the air, and gradually becomes converted throughout into oxide of 

 calcium, or lime. It decomposes cold water rapidly with evolution of 

 hydrogen. Its specific gravity is 1*58. It is moderately hard, 

 malleable, and ductile. It has not been volatilized. When heated to 

 redness in the air, it burns with a scintillating flash ; but, in con- 

 sequence of its want of volatility, does not inflame. Calcium bears to 

 its congeners, strontium and barium, relations similar to those which 

 magnesium bears to its congeners zinc and cadmium ; save that the 

 members of the calcic family are associated rather by an equality, and 

 those of the magnesian family by a gradation of properties. The 

 atomic volume and atomic weight of strontium are respectively the 

 means of the atomic volumes and atomic weights of calcium and 

 barium. Despite many points of resemblance, the differences between 

 calcium and magnesium are well marked. Thus magnesium and zinc 

 are volatile and inflammable metals, permanent in the air, scarcely 

 acted upon by cold water, and obtainable by treating their respective 

 chlorides with sodium. Calcium is neither volatile nor inflammable, 



g2 



