J. W. Gibbs — Vapor- Densities. 383 
error, we en experiments will be necessary to confirm 
the form 
vaonvetill have also been made by M. Wurtz in which 
the vapor of the perchloride of phbophoras was diluted with 
that of the protochloride.t These experiments may be used 
to test equation (8), which, when the values of its constants are 
determined by equation (18), reduces to the form 
' Be is 4 
ai es i 273 13°751, (14) 
where p,, p,, and p, denote the partial pressures due respect- 
ively to the PCI,, the Cl,, and the PCl,, existing as such in the 
once Since these quantities cannot be the sake of 
mmediate observation, a farther transformation of the equation 
will be convenient. Let M,, M, denote the quantities of the 
protochloride and of chlorine of which the mixture ma y be 
formed, and P,, P, the pressure which would belong to sig of 
these if existing by itself with the same volume and tempera- 
ure. These quantities will be connected by the equations 
kt M, kt 
= 5 
Bie sogh . ee pase (9) 
where & denotes the same constant as on page 286. From the 
evident relations 
P.=p,+p,, P,=P, + Pos P=P.TPst Ps 
we ove 
emt —P; ts tas -P,, aes A —P,; 
and by sibdevii: of these ides in dated (14), 
P : P,—p 5441 : 
lox p t 4073 » 16 
log ie PET 13°751 (16) 
Th view of the eoge. (15), this may be regarded as an equa- 
tion between the pressure, the temperature, the volume, and 
ov quantities of protochloride of phosphorus and chlorine into 
Ich the gas-mixture is resolvable. 
"Tt is in Shs form that we shall apply the equation to the 
Table IX of M. Wurtz, the results of which are exhibited in 
The first column gives the number verge ona 
ach experiment in the original memoir; the second, the 
Cale, the nae the observed pressure (p) of the saisctare 
* Adina ts on the de: nsity of this vapor have been made by M 
rg which he says in 1866; “Les déterminations qui je viens 
effectuer & 170 et 172 de bout vers 160 4 165 degrés) m’ont 
nom qui, bien que notablement plus forts que ceux que J ai obtenus 
oe reheat 4 182 et 185 degrés, re - ry el A gps corres- 
vi ; i 
Mh bate: abi. tr aac nents cee carainshioa hase 40% been. poblishod. 
rtain, rmina af 
a gives 6-025 for 170° ot 6-973 for 3535 at atmospheric pressure. The 
; et Tresponding to four volumes is 
ptes Rendus, vol. lxxvi (1873), p. ae 
