HYDRATED PEROXIDE OF IRON. 
33 
ide, instead of being in the state of magma, be used dry, that 
is to say hydrated but not moist, and at a temperature of 36° 
to 40° centigrade, 16 grammes will neutralize about six deci* 
grammes (9.26 grs. troy) of arsenious acid. At least the 
aqueous liquid, resting over 16 grammes cf the hydrated ox- 
ide, which had previously contained 6 decigrammes of arse- 
nious acid for some hours, did not become yellow on the addi- 
tion of a solution of hydro-sulphuric acid, to which a few 
drops of hydro-chloric acid had been added." 
From these remarks it is evident that the dry oxide is not 
so active as that recently precipitated, as less than half the 
quantity of the latter removed the same proportion of arsenious 
acid from solution in about five minutes; indeed, it must be 
evident, that in a case where such feeble affinity is exerted, so 
great a change in the state of aggregation of a substance like 
hydrated oxide of iron as is produced by drying it, and after- 
wards triturating it to powder, would materially interfere with 
combination. To test the matter, however, the following ex- 
periments were made, viz. 
Sixty grains of recently precipitated oxide, dried at a tem- 
perature of from 80 to 90° Fahr., was mixed with water and 
3 grains of arsenious acid in solution added, and the mixture 
occasionally shaken. In half an hour the arsenic was re- 
moved. 
Sixty grains of a dry hydrate, six weeks old, had not re- 
moved, in seven hours, three grains of arsenic; but 120 grains of 
the same oxide separated the same quantity in about four hours. 
Sixty grains of a specimen of hydrated oxide made a year or 
more, had not removed the same quantity of arsenic when ex- 
amined in twenty-four hours; — 120 grains of the same oxide 
removed the arsenic in about ten hours. 
From these observations it is clear that quantity may, to a 
certain extent, make up for quality. They also render it pro- 
bable that if a larger proportion of the specimens J$. B. and 
C. in the first series of experiments had been employed, that 
they would have removed the arsenic sooner, but this does 
VOL. VIII. — NO I. 
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