N atural-Philosophical Collections. 151 
caverns which I have visited,” says Mr. Davy, “ as well as of the specimens 
which have been sent to me from other caves, I believe that they are all similar, 
‘and that the rocks out of which they are hollowed always contain at least carbo- 
nate of lime and feldspar. The decomposition of the latter furnishes the base of 
the salt, and the carbonate, exercising a particular action wpon the oxygen and 
nitrogen of the atmosphere, the nature of which we cannot yet comprehend, gives 
rise to the acid. 
Sect. 3. Nitric acid is formed exclusively by the elements of the atmosphere. 
~ Having shown, in the preceding sections, that saltpetre is found in places far 
removed from any habitation, and in materials which can contain no animal mat- 
ter, M. Longchamp now attempts to prove the impossibility of nitrogen being 
disengaged from this matter to assist in nitrification. 
“ Tt is admitted that the animal matters need not be in contact with the earth, 
“but that their effluvia suffice for the production of saltpetre. Let us, then, try 
all possible suppositions to find out how nitric acid can be formed under these 
circumstances. 
“Ts it formed by nitrogen disengaged from animal matter during putrefac- 
tion ? All chemists know that the products of this putrefaction are ammonia, 
carbonic acid, carburetted hydrogen gas, and perhaps of the gaseous oxide of 
carbon and water, but no nitrogen. But if this gas were produced, how could 
it combine with the chalk ? We have examples of extraordinary combinations 
of gas in its nascent state; but this was not the case of the nitrogen given off 
from blood putrefying at a distance of two feet from the chalk, and produced from 
4 to 5 oz. of saltpetre for each cwt. of chalk, as the commissioners of the Acade- 
my pretend. 
“< Or is it formed by some compound of nitrogen which the effluvia carry along 
with them ? We know that in the putrefaction of blood, urine, &c. all the nitro- 
gen goes to form ammonia; but even admitting that a portion of nitrogen should 
escape from the hydrogen, and form a compound unknown to this day, how does 
it happen that this matter is nitrogen only when it comes in contact with the 
chalk ? for, if it meets with lime, magnesia, alumina, &c. nitric acid is not form- 
ed, or at least only in an insensible degree, and after a long lapse of time. 
“ Or is it the produce of a re-action of the putrid efHuvia upon the atmosphe- 
‘ric air ? Besides the difficulty of conceiving this re-action, and besides the fact, 
that in this case it would be the nitrogen of the air which would form the acid, 
and not that of the animal matter, this unanswerable objection occurs, Why is 
chalk the only body which conduces to this re-action ? 
“ Tt is, then, impossible that there can be disengaged, by putrefying animal 
matter, any substance which by itself, or by its influence, can produce nitric acid ; 
but is it so when this matter is mixed with earth? There is no chemical fact 
which would support the idea, that the products would differ when it is mixed 
‘with earth, and when it is left to putrefy without such admixture.” * 
_ Resting upon these proofs of the incapability of animal matter to the produc- 
tion of nitric acid, it only remained for M. Longchamp to explain the mode by 
‘which he supposed the atmospheric air alone could form this acid; and he states 
his views in the following terms: 5 
“It is universally accorded that nitric acid can only be formed where there is 
a certain degree of humidity, and where the air circulates freely ; for in places 
where it cannot be renewed, there is no formation of the acid. It was thus that 
Lavoisier observed, at Roche Guyon, that in the caverns or holes which were 
deep, and had only one entrance, nitric acid was not discoverable in the depths, 
but near the opening alone. The same observations were made by this celebrated 
chemist in the tufa quarries of Touraine. 
* ¢ Though urine and other similar animal matters, which may be employed 
in moistening nitre beds, cannot serve directly to the formation of nitric acid, 
it is Pe that they may conduce to it indirectly, by preserving their humi- 
dity longer.than pure water:”—-LONGCHAMP, ” 
