being 11:2 and that of periclase 10-9. Although the correspon- 
dence between these protoxyds and the compounds of the two 
classes of oxyds might be regarded as establishing the point, it 
was desirable to add to the series a pure peroxyd. ye 
Such is the martite of Breithaupt which he has described as 
a peroxyd of iron, crystallizing in forms of the regular system, 
and having a specific gravity of 4-65—4-82, which gives an 
atomic volume of 11. These crystals have however been looked 
upon as pseudomorphs after magnetite, and Dana in the last edi- 
tion of his Mineralogy regards their nature as doubtfal. The 
a examining the collection of Dr. Holmes of this city I found 
a specimen which he had received through the late Dr. Horton, 
Munroe, New York, as crystallized ilmenite. Its mon0- 
metric form led me to suppose it to be the octahedral titaniferous 
iron to which the name of iserine has been given,* but on eX 
The titaniferous irons have been described as crystallizing occasionally in forms 
1 same specific gravity as the rhombohedral ney. 
The different formulas cited by Gerhardt give one, three, six and eight equivalents 
of titanate (FeO, TiO2) to one of soninaya, and + ins seober case. But 
se has shown that the ferrous oxyd and titanic acid obtained in the analyses, T& 
sult from the reaction in the process of solution between ioxyd of iron and 
sesquioxyd of titanium, Fe203+4+Tiz0s=2(Fe 0, TiO2).*, If we write the for- 
* See this Journal, [2], vol. ii, p. 33. 
