; Chemistry. XXXV 
hydrocyanic acid, and ammonia, each amounting to the volume 
of the cyanogen absorbed. The first two of these bodies are 
disengaged immediately on the addition of the acid; but the 
ammonia does not make its appearance till there be added an 
excess of lime. Now when the product of the calcination of an 
animal substance with potash is dissolved in cold water, and 
then treated with muriatic acid, and finally, with lime, it exhi- 
bits the same phenomena as the-cyadide of potassium. These 
important facts have been ascertained by M. Gay-Lussac. 
tis important not to throw potash calcined with an animal sub- 
_ stance into water, while red-hot, or even hot; for in that case it 
is decomposed, and a great quantity of ammoniais produced. If 
it be allowed to cool in the open air, it is apt to catch fire, and 
burn like a pyrophorus.—(Ann. de Chim, et de Phys. viii. 440.), 
6. Action of Lron on Water.—It has been generally admitted 
by chemists that iron is capable of decomposing water at the 
ordinary temperature of the atmosphere ; though | am not aware 
that any set of experiments establishing this fact has been pub- 
lished, except those of Lavoisier, which, however, are perfectly 
decisive. This gentleman mixed together iron filings, and 
distilled water, freed from its air by boiling, and placed them 
under a receiver filled with mercury at the ordinary tempera- 
ture of the atmcsphere. Hydrogen gas was evolved in abund- 
ance.—(See Mem. de l’Acad. des Sciences, 1781, p. 478.) 
Dr. Marshall Hall, who does not appear to have been aware of 
these experiments of Lavoisier, nor with the experiments of M. 
Guibourt on the same subject, published in the Journal de Phar- 
macie, for June, 1818 (p. 241), has inserted a paper in the last 
April number of the Journal of the Royal Institution, or of the 
Quarterly Journal, as it has now denominated itself, the object 
of which is to prove that iron has not the property of acting on 
- water deprived of air ; and that in all cases where it was supposed 
to have been oxidized under water, the change was merely the 
consequence of the action of atmospherical air. I have no doubt 
that Dr. Hall made his experiments with sufficient care and pre- 
cision ; yet I think them insufficient to decide the question. He 
put a small quantity of iron into a great quantity of water. Now 
{ happen to have made similar experiments to his many years 
ago. I found that in such cases no sensible quantity of hydrogen 
was extricated after an interval of several weeks ; but if the mx- 
ture was kept for some hours at the boiling temperature, I always 
obtained a sufficient quantity of hydrogen to ascertain its nature. 
M. Guibowt, in his paper above alluded to, has gone much 
further, and indeed placed the subject in a very clear point of 
view. When a small quantity of water is mixed with a great 
quantity of iron, the decomposition of that liquid goes on rapidly ;. 
but when a great quantity of water is mixed with a small quan- 
tity of iron, no sensible decomposition takes place unless the 
temperature be considerably elevated. 
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