PRUSSIC ACID, ANTIMONY, AND ARSENIC. 
143 
the very pulpy state of hydrate, thrown down from very dilute cold solutions 
of peroxide of iron by ammonia, but we have found that it is of very little 
consequence, whether the oxide be thrown down from strong or weak, hot or 
cold solutions or whether by ammonia or a carbonated alkali; if, under any 
of these circumstances, the hydrate be used before being dried, it is almost 
equally effectual in absorbing the poison; if, however, the oxide should have 
been dried, it no longer acts; it does not appear to have the least power of 
removing arsenious acid from a liquid. 
We have found, however, that 100 grs. of dry peroxide of iron, if sub¬ 
jected to most careful pulverization and elutriation, remove rather more than 
2 grains of arsenious acid from solution. 
The hydrate already prepared, and kept under water for some months, 
loses its absorbing action gradually (slowly at first, but in an increasing ratio 
afterwards), so that, after four months, its power is not more than half of 
what it originally was; and, after five, its absorptive action is diminished to 
about a fourth. 
That we might be able to make a definite statement of the time in which 
the hydrated peroxide of iron could be precipitated, washed, and made ready 
for use, we threw down, with excess of ammonia, a quantity of the solution 
of perchloride of iron, containing 80 grs. of anhydrous peroxide oi iron, 
after mixing it with ten ounces of water at a heat of about 120° F. 
The precipitate settled quickly, but we did not wmit for subsidence, so as 
to effect the washing by decantation, but at once threw' the whole upon a 
filter, and washed the precipitate with pure water till the washing water 
passed through tasteless. The operation was finished in twenty minutes. 
The drained hydrated oxide was found to weigh exactly 4| oz. On now' 
mixing, in a beaker, the hydrated oxide thus obtained with 10 grs. of 
arsenious acid in solution, carefully agitating for a few' minutes, and then 
separating the liquid by filtration, sulphuretted hydrogen water added to 
the filtered liquid, acidulated with a few' drops of muriatic acid, failed to 
show the presence of the slightest trace of arsenic, ihe whole operation 
was terminated within half an hour. 
Three points worthy of special remark are brought out by this experi- 
lst. The short time required for the preparation of the antidote, the solu¬ 
tion of perchloride of iron being alwmys ready at hand. 
2nd. The remarkable bulk of the hydrated oxide of iron, in the only state 
in which it should be used as an antidote for arsenious acid. Although the 
hydrate used contained only 80 grs. of dry peroxide of iron; yet, in the 
state of hydrate, the weight was actually 4^ oz. avoirdupois. ; the oxide 
of iron retaining a quantity of water equal to twenty-one times its own 
weight. .. « _ -j /-vQ 
3rd. Although the oxide was thrown down at a heat not less than 110 x 
yet it was capable of entirely removing 10 grs. of arsenious acid from solu¬ 
tion in water. . _ „. , 
We have stated that 80 grs. of peroxide of iron, m the form of hydrate, 
absorb 10 grs. of arsenious acid in solution ; but we have found that, if time 
is given, its absorbing power is nearly doubled. . 
On mixing 10 grs. of arsenious acid, dissolved in water, with the pro¬ 
perly prepared hydrate of 80 grs. of peroxide of iron, stirring briskly for a 
few minutes and filtering, not a trace of arsenious acid can be found m the 
filtered liquid. If the filter, with its contents, be now mixed with, a solu¬ 
tion of an additional 5 grs. of arsenious acid, and the liquid, after proper 
stirring, be filtered away, the presence of arsenious acid can be proven in it 
at once; but if the stirring has been continued for a long time, and twelve 
