581 



CHAPTER XIV 



THE VALENCY AND SPECIFIC HEAT OP THE METALS. MAGNESIUM. 

 CALCIUM, STRONTIUM, BARIUM, AND BERYLLIUM 



IT is easy by investigating the composition of corresponding com. 

 pounds, to establish the equivalent weights of the metals compared with 

 hydrogen that is, the quantity which replaces one part by weight of 

 hydrogen. If a metal decomposes acids directly, with the evolution of 

 hydrogen, the equivalent weight of the metal may be determined 

 by taking a definite weight of it and measuring the volume of hydrogen 

 evolved by its action on an excess of acid ; it is then easy to calculate 

 the weight of the hydrogen from its volume. 1 The same result may be 

 arrived at by determining the composition of the normal salts of the 

 metal ; for instance, by finding the weight of metal which combines 

 with 35-5 parts of chlorine or 80 parts of bromine. 2 The equivalent of 

 a metal may be also ascertained by simultaneously (i.e. in one circuit) 

 decomposing an acid and a fused salt of a given metal by an electric 

 current and determining the relation between the amounts of hydrogen 

 and metal separated, because, according to Faraday's law, electrolytes 

 (conductors of the second order) are always decomposed in equivalent 

 quantities. 2 bi3 The equivalent of a metal may even be found by simply 



1 Under favourable circumstances (by taking all the requisite precautions), the weight 

 of the equivalent may be accurately determined by this method. Thus Reynolds and 

 Bamsay (1887) determined the equivalent of zinc to be 32'7 by this method (from tho 

 average of 29 experiments), whilst by other methods it has been fixed (by different 

 observers) between 32*55 and 33'95. 



The differences in their equivalents may be demonstrated by taking equal weights of 

 different metals, and collecting the hydrogen evolved by them (under the action of an 

 acid or alkali). 



2 The most accurate determinations of this kind were carried on by Stas, and will be 

 described in Chapter XXIV. 



3 Bis The amount of electricity in one coulomb according to the present nomen- 

 clature of electrical units (see Works on Physics and Electro-technology) disengages 

 0-00001086 gram of hydrogen, 0'00112 gram of silver, 0-0003263 gram of copper from the 

 salts of the oxide, and 0-0006526 gram from the salts of the suboxide, &c. These amounts 

 stand in the same ratio as the equivalents, i.e. as the quantities replaced by one part by 

 weight of hydrogen. The intimate bond which is becoming more and more marked 

 existing between the electrolytic and purely chemical relations of substances (especially 

 in solutions) and the application of electrolysis to the preparation of numerous substances 



