32 
HYDRATED PEROXIDE OF IRON. 
for two hours with water in which sixteen grammes (247 
grains) of colcothar is suspended, the filtered liquid will still 
afford arsenic by means of Marsh's apparatus, and hence 
that 833 times the weight of the acid will not neutralize it. 
Is it not probable that the true reason of the deterioration of 
the preparation will be found in a combination of the oxide 
and water when recent, which does not exist in that which has 
been long kept ? That the presence of water is a condition 
of its activity, has been shown by the experiment of Orfila, 
quoted above. To ascertain, if possible, whether the hydrate 
long kept (under water) had the same amount of water in its 
composition as that recently precipitated, four specimens were 
taken from those previously used, viz. : A, C, E, and I. The 
two first, four and two years old, the two last nine months old 
and recent. They were dried at a temperature of from 80° 
to 90° Fahr., for twelve hours, a given quantity of each was 
introduced into glass bulbs afterwards balanced, and then sub- 
jected to a red heat, until they ceased to lose weight The loss 
was in the following proportion, 
A, 8.4 
C, 7.2 
E, 12. 
I, 13. 
These experiments were repeated with nearly similar re- 
sults. This statement shows that the recently precipitated 
oxide contains nearly double the amount of water that is con- 
tained in the two first, and more than is in the third. Whe- 
ther the proportion of water combined with the oxide is a 
condition of its activity or not, the above statement, taking 
either view of the subject, is a curious coincidence; the 
proportion of water being very nearly that of their activity, as 
seen by reference to the previous experiment. 
Orfila further says in the paper before alluded to, " I have 
proven by numerous experiments, that if the hydrated perox- 
