INTENSITY OF MAGNETIC AND DIAMAGNETIC FORCES. 725 



intensity of the current being constant, the force with which 

 these substances are attracted by the electro -magnet is the relative 

 measure of their magnetism. If we divide it by the weight of 

 the substances, we obtain numbers which represent the relative 

 intensities of the magnetism of these substances /or equal weights. 



We here enter upon a new field of physical investigations, and 

 a number of questions arise, the answers to which are of mani- 

 fold interest, — questions which partly encroach upon the pro- 

 vince of chemistry. Hitherto I have only been able to procure 

 pure oxide of nickel, but not pure nickel itself, nor the other 

 magnetic metals except ii'on. My investigations must therefore 

 first be confined to iron and its chemical compounds. In what 

 proportion is the original magnetic force of the iron diminished 

 when oxygen is added to it to form the peroxide ? how, again, 

 when water is added to the oxide as in the hydrate ? when the 

 oxide has combined with different acids to form salts? What 

 relations do the salts of the peroxide hold to those of the pro- 

 toxide ? What must the chemical composition of a salt contain- 

 ing iron be so that it may cease to be magnetic ? 



17. I shall first communicate the results of two series of expe- 

 riments, which may be condensed into one, because the electro- 

 magnetism, which was excited by six Grove's elements, was in 

 each case of the same intensity, and made but very slight varia- 

 tions. The weighings were not made until in each case the bat- 

 teiy had been in action for some time, and after each weighing 

 the circuit was opened. The first series of experiments related 

 to aqueous solutions of salts of iron. I took — 1. pernitrate of 

 iron, which had been prepared by pouring excess of concentrated 

 nitric acid upon the peroxide of iron denoted by II. ; 2, per- 

 chloride of iron prepared from the same oxide with concentrated 

 hydrochloric acid ; 3, dry neutral persulphate of iron from the 

 chemical laboratory, which dissolved very slowly in water ; 4 

 and 5, protochloride and protosulphate of iron, prepared on the 

 morning of the performance of the experiment by pouring hy. 

 drochloric and sulphuric acid upon finely-divided iron : all the 

 solutions except the latter were saturated. The watch-glass 

 described in the second paragraph was filled with the differ- 

 ent solutions in succession, and subsequently the amount of iron 

 contained in that quantity of each of these solutions which was 

 used in the experiment was determined. The attraction of the 

 solutions by the electro-magnet was compared with the attrac- 



