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SELECTED ARTICLES. 
This process is as simple as that which consists in treating 
the hydrochloric solution of the two oxides by sulphurous 
acid, and ascertaining by the aid of the muriate of baryta, the 
quantity of sulphuric acid which results from the change of 
the protoxide into the peroxide of iron. It is likewise a more 
convenient process, when acting upon a silicate soluble in the 
hydrochloric acid, for on treating the solution of the two 
oxides, by means of the sulphurous acid, it is very difficult to 
separate the sulphate of baryta produced, from the gelatinous 
silica with which it is mixed. 
Likewise there are certain minerals in which iron appears 
to be in the state, partly of protoxide and partly of peroxide, 
which are not soluble in hydrochloric acid, while they 
readily dissolve in nitromuriatic acid. We have, then, no 
direct means to determine the relative proportions of the two 
oxides. I allude in this remark to Wolfram. Yauquelin 
has analyzed a variety of this mineral, coming from the de- 
partment of Haute-Vienne, and he supposes that the iron ex- 
ists in it, one-half in the state of protoxide, the other half as 
peroxide, [Treatise on Analysis by the Dry Way, Vol. II., 
p. 264.) By using, instead of the nitromuriatic acid, the 
hodrochloric acid, and acting upon a mixture of this mineral 
and peroxide of manganese, in the manner which I have 
pointed out, we may easily ascertain the relative proportion 
of the two oxides. 
Two atoms of the protoxide of iron, 2 Fe =878.40, absorb 
one atom of oxygen = 100 in passing to the state of per- 
oxide Fe. 
Thus a difference of 145S.09 in the weight of sulphate of 
baryta obtained, corresponds to 879.40 of protoxide of iron. 
One of sulphate of baryta corresponds to 0.602 of protoxide 
of iron. 
4. We may verify in a convenient manner the laws of 
composition of a great number of metallic salts, by comparing 
the total quantity of oxygen absorbed, with that which re- 
mains combined, as an electro-negative element in the solu- 
tion. I will state, for example, an examination which I made 
