THE VALENCY AND SPECIFIC HEAT OF THE METALS 595 



chloride with the vapours of potassium. At the pressnt time (Deville's 

 process) magnesium is prepared in rather considerable quantities by a 

 similar process, only the potassium is replaced by sodium. Anhydrou* 

 magnesium chloride, together with sodium chloride and calcium fluoride, 

 is fused in a close crucible. The latter substances only serve to facili- 

 tate the formation of a fusible mass before and after the reaction, which 

 is indispensable in order to prevent the access and action of air One 

 part of finely divided sodium to five parts of magnesium chloride is 

 thrown into the strongly heated molten mass, and after stirring the 

 reaction proceeds very quickly, and magnesium separates, MgCl 2 4- Na 2 

 = Mg -f 2NaCl. In working on a large scale, the powdery metallic 

 magnesium is then subjected to distillation at a white heat. The dis- 

 tillation of the magnesium is necessary, because the undistilled metal is 

 not homogeneous 14 and burns unevenly : the metal is prepared for the 

 purpose of illumination. Magnesium is a white metal, like silver ; it 

 is not soft like the alkali metals, but is, on the contrary, hard like the 

 majority of the ordinary metals. This follows from the fact that it 

 melts at a somewhat high temperature namely, about 500 and boils 

 -at about 1000 It is malleable and ductile, like the generality of 

 metals, so that it can be drawn into wires and rolled into ribbon ; it is 

 most frequently used for lighting purposes in the latter form. Unlike 

 the alkali metals, magnesium does not decompose the atmospheric 

 moisture at the ordinary temperature, so that it is almost unacted on 

 by air ; it is not even acted on by water at the ordinary temperature, 

 so that it may be washed to free it from sodium chloride. Magnesium 

 only decomposes water with the evolution of hydrogen at the boiling 

 point of water, 15 and more rapidly at still higher temperatures. This 

 is explained by the fact that in decomposing water magnesium forms 

 an insoluble hydroxide, MgH 2 2 , which covers the metal and hinders 

 the further action of the water. Magnesium easily displaces hydrogen 

 from acids, forming magnesium salts. When ignited it burns, not only 

 in oxygen but in air (and even in carbonic anhydride), forming a white 

 powder of magnesium oxide, or magnesia ; in burning it emits a white 

 and exceedingly brilliant light. The strength of this light naturally 

 depends on the fact that magnesium (24 parts by weight) in burning 



14 Commercial magnesium generally contains a certain amount of magnesium nitride 

 (Deville and Caron), Mg 3 N 2 that is, a product of substitution of ammonia which is 

 directly formed (as is easily shown by experiment) when magnesium is heated in nitrogen. 

 It is a yellowish green powder, which gives ammonia and magnesia with water, and 

 cyanogen when heated with carbonic anhydride. Pashkoffsky (1893) showed that Mg 3 N s 

 is easily formed and is the sole product when Mg is heated to redness in a current of NHj. 

 Perfectly pure magnesium may be obtained by the action of a galvanic current. 



15 Hydrogen peroxide (Weltzien) dissolves magnesium. The reaction has not been 

 investigated- 



