405 
In conclusion one of the few applications of the second kind may 
be briefly mentioned here. 
In my first communication *) concerning the system hydrogen sul- 
phide-water I have fully determined the situation of the quadruple 
point S (hydrate) by the side of two liquids (Ls, and L,) and gas (G) 
with the three-phase lines terminating there. If this rule had been 
known to me already then, I could have directly inferred from the 
figure of the cited communication that between the three-phase lines 
S+1L,+6G and S—+L, + 1, no metastable prolongations occur, that 
there the coexistences : 
S+ 1h, (angle < 180° between S+1L,+G and SHL, + Li) 
BRG i » o+h,+G and L, + L, +G) and 
S+ 1, te 53 » o+h,+G and S+L, + Li) 
occur, and that therefore the order of the phases must be GL,SL,, if 
the mentioned coexistences are to take place between phases that 
are consecutive in concentration. The gas of these phases containing 
the greatest quantity of hydrogen sulphide, it is clear that the 
hydrate contains less water than L,, and that therefore the liquid 
L, lies on the side of the water. From determinations which I 
carried out later on, and which I have communicated in my second 
paper ®) on this system it appears that this conclusion is really valid. 
Anorganic Chemical Laboratory of the University. 
Amsterdam, September 18, 1912. 
Physics. — “J/sotherms of diatomic substances and of their binary 
mixtures. XI. The compressibility of hydrogen vapour at, and 
below, the boiling point” By H. Kamertincu Onnes and W. 
J. DE Haas. Communication N°. 127e from the Physical Labo- 
ratory at Leiden. 
(Communicated in the meetings of May 25 and June 29, 1912), 
$ 1. Jntroduction. To the region covered by the investigations 
which have been made for many years past in the Leiden laboratory 
upon the equation of state for hydrogen at low temperatures (for 
the latest paper see Comm. N°. 100a, Proc. Dee. 1907) the present 
Communication adds the region for hydrogen vapour lying between 
—252° C. and —258° C. While the lowest reduced temperature 
1) These Proc. January. 1911. p. 829. 
2) These Proc. June. 1911. p. 195. 
