932 
Curve (L) = A + B+Iee+G=(M)+ A+ Bhas to coincide 
also with the (1/)-curve, but it goes, starting from g towards lower 
temperatures. 
Curve (J) =A+L6+L+4+G goes starting from gq, also 
towards higher temperatures, but it must be situated below the 
curves (A) and (B). In order to show this latter we take again the. 
three points 7, s and ¢ in fig. 1. As the vapour-pressure. increases, 
starting from s, along the isotherms rs and fs, the curves (A) and 
(B) must be situated, therefore, in fig. 3 above curve (1). | 
Those considerations are also valid when we replace the compo- 
nents A and B by their hydrates A, and B,, provided that solution 
q is situated within the triangle W A, B, and not too close to the 
line A„ B, When this is really the case, then we are able to define 
the directions of the curves in the same way as e.g. in Comm. XIII. 
Leiden, Inorg. Chem. Lab. (To be continued). 
Physics. — “On the equation of state of water and of ammonia” 
By G. Horst. Supplement N°. Hf to the Communications. 
from the Physical Laboratory at Leiden. (Communicated by 
Prof. H. KaAMERLINGH ONN#s). 
(Communicated in the meeting of January 27, 1917). 
In an investigation published some time ago ‘on the equation of 
state of methylchloride- and ammonia‘), it was shown that the sign 
of the coefficient C of KaMERLINGH ONNES’s © equation of state 
Be Oes Doe Ha pk 
pesRI(1$ = 454045 elas a 
v v 7) 
was different for the two substances; for ammonia it was negative; 
for methyl chloride, as for other normal substances, C was found 
to be positive. At that time I ventured the hypothesis C would be 
found negative for other associating*) substances. Following this 
idea L have calculated B and C for water vapour, starting from 
the data given by M. Jacop*) in tables 7 and 8 of his paper on 
1) G. Horsr. Comm. Leiden No. 144. 
*) See for instance H. KAMERLINGH ONNES and W. H. Keesom. Enc. d. Math. 
Wiss. Art. V 10 p. 728. also Comm. Leiden Suppl. 23. 
5) Comp. Enc. p. 722, where it is pointed out that besides the associating 
(polymerized) substances, others occur (deviating substances) which show similar 
deviations as the first. 
4) M. JacoB. Zeitschr. Ver. D. Ing. 1912 p. 1980. 
