286 J. W. Gibbs — Vapor-Densities. 
7 s 
fournies instantaném 
It is not difficult to form an estimate of the quantities of heat 
which come into play in such cases. With respect to peroxide 
of nitrogen, it was estimated in the paper already cited that the 
heat absorbed in the conversion of a unit of N,O, into NO, 
under constant pressure is represented by 7181 a. (The heat 
is supposed to be measured in units of mechanical work). 
Now the external work done by the conversion of a unit o 
N,0, into NO, under constant pressure is a,¢. Therefore, the 
ratio of the heat absorbed to the external work done by the 
conversion of N,O, into NO, is 7181+¢, or 23 at the tempera- 
ture of 40° centigrade. Let us next consider how much more 
rapidly this vapor expands with increase of temperature at con- 
stant pressure than air. From the necessary relation 
kmt 
=?pDd’ 
duire et la dilatation et la décomposition ne sauraient étre 
ent.””* 
v 
where m denotes the weight of the vapor, and & a constant, we 
obtain 
(F en Mtn ® (2) 
dt}/p t D\dt/,’ 
where the suffix p indicates that the differential coefficients are 
] . 
for constant pressure. The last term of this expression evi- 
dently denotes the part of the expansion which is due to the 
volume of air under the same circumstances. e ratio of the 
: t/d | 2 
two terms is -(> , the numerical value of which for the 
Pp 
temperature of 40° is 2°42, as may be found by differentiating 
equation (10), or, with less precision, from the numbers in the 
third column of Table L oS 
40° and the pressure of one atmosphere receive equal sage 
* Comptes Rendus, t. lx, p. 730. 
eS 
“be: ieee ache Pea siraeiics 
a 
