Proceedings of the Eoyal Irish Academy. 



X. — LlEOEATOET XoiES.^ Bv ChAELES E. C. TlCHBOIl]S^E, Ph. D., 



r;c.s., &c. 



iN'o. 6. — Ox THE FoKiiATiox OP IEagkttic Oxide bt the Dissociation 



OF PsEEors Salts. 



[Eead, Apiil 23, 1877.] 



Ix the description of a find of magnetic iron ore in Wicklo^r, -n-hich I 

 read before the Eoyal Geological Society of Ireland, I lately oifered 

 some suggestions as regards the processes by which these deposits 

 ■were formed in such localities ; the stratified appearance of the ore, 

 taken in connexion with its associated minerals, at once putting 

 out of question the idea of this magnetite being of igneous origin. 

 There was, however, undoubted evidence of the ore being the result 

 of the oxidation of pyrites into sulphates of the base. Presuming that 

 there is no limestone in tliis district, it becomes necessary to suppose 

 that the deposition of PesOjt was determined without the aid of a pre- 

 cipitant. At the time of my reading the Paper to which I have 

 referred, I exhibited a tube, which originally contained a partially 

 oxidized solution of ferrous sulphate (a solution of ferrous sulphate 

 which had been exposed to the air for some twenty-four hours). On 

 submitting this tube, when sealed, to a temperature considerably 

 above the boiling-point of water, magnetic oxide was deposited, appa- 

 rently in the anhydi'us state. On repeating this experiment lately, 

 with definitely oxidized solutions, to my great sui'prise I got nothing 

 but an anhydrus red precipitate of ferric oxide, perfectly desti- 

 tute of magnetic properties. I therefore instituted experiments to 

 determine the conclitions under which FcoOi, would be deposited. 



A mixture was made, which, on precipitation, would give us the 

 molecule PeO, Pcj, Pes, or one in which two-thirds of the solution had 

 been oxidized up to the ferric condition. On heating this solution 

 nothing but ferric oxide was formed. 



In one case half the solution had been converted into a ferric, and 

 half left as a ferrous salt. Such a solution contained the elements of 

 an oxide 2PeO, Pcj, P3. Only peroxide of iron was obtained in this 

 case also, even after prolonged heating at a very high pressure in 

 sealed tubes. As I thought that the basicity of the solutions might 

 determiae the deposition of the magnetic oxide, both of the above 

 solutions were rendered so basic that the slightest application of heat 

 would determine a precipitate on heating. On submitting them to a 

 very high temperature in sealed tubes the deposits were not magnetic, 

 and, therefore, we must come to the conclusion that, owing to the 

 easy dissociation of ferric oxide, that oxide is deposited first, and that 

 the acidity of the solution produced by this act of dissociation is suffi- 

 cient to keep the ferrous oxide in solution. There is no doubt that a 



^ Continued from vol. ii., series ii., p. 84. 



