190 On the Chemical Compounds of (Marcu, 
been entirely abandoned by their author, as will be seen in the 
sequel. 
Mr. Davy, in his Researches in 1800, published the result of an 
interesting experiment on the combination ef oxygen and nitrous 
gas, the former being in excess, in a receiver previously exhausted. 
He found that one measure of oxygen united in these circumstances 
to nearly 2°2 of nitrous gas. In 1810 I published the results of 
eight similar experiments, made by varying the ratios of oxygen 
and nitrous gas so as to have each of them more or less in excess. 
By this method I found that the union of oxygen and nitrous gas 
was subject to great vicissitudes as well as in eudiometric tubes. 
One measure of oxygen united with 1°44 nitrous gas as a minimum, 
and with 2°29 as a maximum, in these eight experiments. 
Sir Humphry Davy in 1812 gives an account of repeated expe- 
riments on the combinations of oxygen and nitrous gas in exhausted 
vessels, though the particulars are not detailed; from which he 
infers that the acid obtained from mixtures of nitrous and oxygen 
gas over water is never saturated with oxygen, and that the true 
nitric acid consists of one measure oxygen and 1+ nitrous gas (that 
is, 1*5 oxygen and two nitrous); he further infers that one volume 
oxygen and two nitrous gas constitute 14 volume of nitrous acid gas. 
He allows that one measure oxygen unites in certain circumstances 
with from two to three measures of nitrous gas; but has given no 
name to this last compound. The limits of combination he con- 
sidecs as one oxygen to J+ nitrous as a minimum, and to thrée 
nitrous asa maximum. ‘This, as may be seen, agrees nearly with 
my previous determination ; but differs materially from Gay-Lussac’s 
as far as regards the minimum of nitrous gas. One of the above 
observations of Davy appears to me important, and, as far as I 
know, original ; namely, that nitric acid is constituted of oxygen 
and nitrous gas, the latter being a minimum according to the 
methods at present known of uniting them. This notion, I appre- 
hend, is correct; and it has since, as will be seen, been adopted 
and confirmed by Gay-Lussac. Davy suggests, with probability, 
that nitric acid cannot be exhibited in the form of a permanent 
elastic fluid, but always requires some base, as water, an alkali, &c. 
as necessary both for its formation and preservation. In this respect 
it seems to me analogous to the sulphuric and muriatic acids. 
Vhough differing from Gay-Lussac in regard to some of the com- 
pounds of azote and oxygen, he agrees with him in others, and 
seems in general to adopt the notion of gases uniting in volumes 
of simple ratios. 
In regard to nitrous oxide, Davy agrees with Gay-Lussac that 
one volume of it contains one of azote and half a volume of 
oxygen ; yet he states the specific gravity of nitrous oxide such that 
100 cubic inches weigh 48 or 49 grains, whereas they ought to 
weigh 461 grains from his own data of the composition of the gas. 
There must, therefore, be an crror somewhere in this statement. 
2 
