1817.) Royal Academy of Sciences. 477 
by Gay-Lussac, it follows that nitrous gas contains a volume of 
azote and an equal volume of oxygen without condensation; that in 
certain circumstances there combines a volume of azote with a 
volume and a half of oxygen, to which Gay-Lussac gives the name 
of pernitrous acid; that common nitrous acid is composed of one 
volume of azote united to two volumes of oxygen; and that nitric 
acid is composed of one volume of azote united to two volumes and 
a half of oxygen. 
Among these different varieties (if we may so express ourselves) 
of oxides or acids which have azote for their radical, there is one 
obtained by the distillation of neutral nitrate of lead previously 
dried. It is a very volatile liquid, of an orange colour. Gay- 
Lussac considered it as nitrous acid, the elements of which were 
kept united by means of a quantity of water which constituted a 
part of it. But M. Dulong has ascertained by very exact analyses 
that it contains no water, and on that account has given it the name 
of anhydrous nitrous acid. His result has been confirmed by syn- 
thesis. One volume of nitrous gas, and a little more than two 
volumes of oxygen gas, exposed to an artificial cold of — 4°, 
forms this acid, which, among other properties, changes colour, not 
only by being mixed with water, but likewise by heat. At — 4° it 
is colourless, at 59° it becomes orange, and at 82° almost red. Four 
parts of nitrous gas and one part of oxygen gas, condensed in the 
same way by cold, formed a deep green liquid, much more volatile 
than the preceding liquid, which M. Dulong considers as a simple 
mixture of nitrous acid and another acid in which the proportion of 
nitrous gas is much greater. 
M. Dulong has examined likewise the proportions in which 
oxygen combines with phosphorus to form acids. Before him only 
two acids had been admitted. His researches have induced him to 
believe that there are four. That which contains the least oxygen 
is obtained by throwing an alkaline phosphuret into water. Phos- 
phureted hydrogen is disengaged, and the oxygen of the water 
forms with the remaining phosphorus an acid which remains com- 
bined with the alkali, and which may be separated by sulphuric 
acid. M. Dulong calls it hypo-phosphorous acid. But he is of 
opinion that hydrogen enters into it as a constituent. 
A second acid, to which M. Dulong gives the name of phos- 
phorous, is obtained by decomposition ot water when proto-chloride 
of phosphorus is put into that liquid. Two acids are formed, 
namely, the muriatic and this of which we are speaking. M. 
Dulong is of opinion that it is a compound of 100 parts of phos- 
phorus and 75 of oxygen. 
The third acid is that which is produced by the slow combustion 
of phosphorus in the air. It is decomposed when saturated into 
phosphoric and phosphorous acids, and gives at the same time phos- 
phites which are more soluble, and phosphates which are less so. 
However, M. Dulong does not regard it as a simple mixture, but 
rather as a combination of these two acids, having some resem- 
