314 M. Ebelmen on 



But M. Ebelmen has not limited himself to the crystallisa- 

 tion of infusible substances. The means he conceived hav- 

 ing been completely successful, he applied them to a different 

 class of considerations, namely, to remove any doubt that 

 might remain as to the composition of certain minerals, and 

 clearly to establish analogies which hitherto rested only on 

 conjecture. His first experiments having confirmed the com- 

 position AP 0^, Mg for spinel, he wished to ascertain if 

 its presumed isomorphisms could be substituted for the mag- 

 nesia, and those of alumina could be substituted for that sub- 

 stance. This the natural compositions would lead us, on 

 theory, to suppose, but the fact had never been clearly de- 

 monstrated. 



For the magnesia, therefore, he successively substituted 

 lime, protoxide of manganese, protoxide of iron, and protox- 

 ide of cobalt, and he obtained, if not alvvaj'S bodies crystal- 

 lised in distinct regular octohedrons, at least bodies present- 

 ing positive indications of this form — the hardness, and all 

 other characters like those of other spinels. He mingled 

 many of these composites together, and the results were the 

 same as when employing the magnesia alone. With regard 

 to the substitution of baryte in the same proportional rela- 

 tions, it has yielded rather vague indications of crystallisa- 

 tion, but evidently belonging to another system, and resem- 

 bling the result which the author had previously obtained by 

 employing glucine, which produced cymophane artificially, 

 in all respects identical with the natural substance, the com- 

 position of which, previously considered very probable, was 

 thus completely verified. 



M. Ebelmen proceeded in the same manner by replacing 

 the alumina by its presumed isomorphisms, namely, the oxide 

 of chrome Cr'^ 0^, the peroxide of iron, &c., in the atomic 

 proportions of spinel, sometimes preserving the magnesia 

 as a base, at other times substituting other bodies for it. In 

 all his experiments he obtained matters completely analo- 

 gous to the aluminate of magnesia, and, among others, the 

 chromate of iron, quite analogous to spinel, thus removing 

 all doubts on what has been called chromated iron or sidero- 

 chrome. He has likewise ascertained that mixtures of these 



