456 Experiments made at the Polytechnic Schoot 
Jaft portions difplaced, that we might fubjeét them to a — 
eudiometric proof. 
With this view we employed 18 decagrammes (about fix 
ounces) of the oxygenated muriat of pot-afh, which were put 
into a retort, at once to furnifh, at one operation, the wholé 
quantity of the gas neceffary for this renewal. 
Thofe who havé not tried themf€lves' this method of fub- 
ftituting one aériform fluid for another, might entertain fome 
doubt refpecting the purity of that employed in our experi- 
ment; but it will be ealy for me to remove it. ‘This was an 
article of fo much importatice that we could not neglect at- 
tempting to colleé proofs of it. 
We know with what fuccefs M. Humboldt applied to the 
improvement of eudiometry, ‘The intereft which he took in 
our experiment induced me to invite him to come and deter- 
mine himfelf with thofe inftruments, and by thofe proceffes, 
which were familiar to him, the purity of the oxygen gas in 
which the combuftion was to take place. He readily ac- 
cepted my invitation, as I had reafon to expeét, from his well 
known zeal for the progrefs of fcience; and this article of 
our report is the production of his pen. I-had likewife the 
fatisfaction of fecing him apply eudiometric inftruments to 
the examination of the refiduum of the gas after the com- 
buttion. The following is the refult of the proofs to which 
he fubjeéted that introduced into the apparatus to ferve far 
the combuftion:— 
Nitrous gas, difengaged, by means of copper, from weak 
nitric acid, was tried’ with fulphat of iron and oxygenated 
muriatic acid, which fhewed in it from o’og to 0'10 of azot. 
One hundred parts of oxygen gas received, towards the mid- 
dle of the operation, as it iffued from the globe, in which we 
had propofed to difplace; in fucceffion, common air by oxygen 
gas, were mixed with 300 parts of this nitrous gas: there 
was an aériform refiduum of 0°66: making allowance for 
027 or 0°30 of azot, pre-exifling in the nitrous gas, we 
judged that, in 100 parts of gas tried, there were flill 36 of 
azotic gas. 
We then continued to introduce into the globe frefh oxy- 
gen gas. We colle&ted towards the end a portion which was 
- 9 ; fubjected 
ee 
+ Boe 
ow 
