TicHBOUXE — Laboratory Notes. 71 



point would ultimately be rcaeliecl wliere the dyad iron would be de- 

 posited if we could get tubes sufficiently strong to stand the pressure, 

 but they invariably burst. The presence of alkaline salts, although 

 they facilitate the deposition of basic precipitates, did not in this case 

 determine the formation of magnetic oxide. 



A solution of ferrous sulphate was allowed to remain exposed 

 to the air for some time until i:)ai'tially oxidized. The resulting 

 solution was then placed in a sealed tube, and on the application 

 of heat it immediately deposited the magnetic oxide, and apparently 

 in a larger proportion than what would be deposited fi'om the small 

 amount of trioxide formed. "VYe, therefore, see that mixtures such 

 as would give the oxide FeaO^, on precipitation by an alkali, or 

 alkaline earth, do not give magnetic oxide when submitted to the 

 dissociative action of heat, or at least they do not do so under the 

 pressure that we are enabled to bring to bear. But we also find that 

 partially oxidized solutions of ferrous salts, containing 10 to 20 per 

 cent, of the ferric oxide, do deposit magnetic oxide, on submitting 

 thetn to heat under pressure, although such a solution on being left 

 exposed to the air would not deposit anything but ferric oxide. 

 Even if a ferrous salt is directly precipitated, in time the ferrous 

 oxide is formed, but never the intermediate magnetic oxide. On the 

 application of a temperature above 100 C, magnetic oxide is deposited 

 fi'om solutions which are slightly oxidized. 



Assuming that pyrites is the origin of this vein of magnetic ore, 

 we should get by the weathering action of the air a solution which 

 would exactly answer all these rec[uisites — a ferrous sulphate partially 

 oxidized, and in a basic condition. Magnetic oxide is found exten- 

 sively diffused, and in immense masses, in all parts of the world. It 

 can be formed by igneous action, and is no doubt frequently formed by 

 the precipitating action of alkaline earths ; but there are certain de- 

 posits which from their character do not point to either of those 

 methods ; and I have, I think, supplied in this note a description of 

 one of the methods by which magnetite is sometimes formed in the 

 laboratory of IS'ature. 



