( 321 ) 
A more exact method may perhaps give numbers from which a 
better formula might be deduced, and which at the same time might 
give us some insight in the phenomenon. 
I have tried to get more exact numbers by means of the Kunpr 
dust-figures but I did not succeed, though others might. Yet the 
oscillatory discharge of a Leyden jar through an inductive resistance 
easily gave regular dust-fieures. The reason why the Kunpt-method 
proved refractory with the singing are, is not easy to be understood: 
Lean only suppose that the intensity of the sound is not large enough. 
Physics. — Dr. J. E. VeRSCHAF EELT. “ Contributions to the knowledge of 
VAN DER Waals’ w-surface. VIL. The equation of state and 
the w-surface in the immediate neighbourhood of the critical 
state for binary mixtures with a small proportion of one of 
the components”. Communication n°. 81 from the Physical 
Laboratory at Leiden, by Prof. H. KAMERLINGH ONNES. ') 
(Communicated in the meeting of June 28, 1902). 
Introduction. 
In Communication n°. 65 from the Physical Laboratory at Leiden *) 
I have given the first results of a treatment of my measurements on 
mixtures of carbon dioxide and hydrogen *) by the method which 
KAMERLINGH ONNES *) alone and with ReINGANUM *) used for the 
measurements of KUENEN on mixtures of carbon dioxide and methyl 
chloride ®). They confirm KAMERLINGH OnNEs’ opinion that the isothermals 
of mixtures of normal substances may be derived, by means of the 
law of corresponding states, from the general empirical reduced 
equation of statefor which he has given in communications nrs. 71 7) 
and 74°) a development in series indicated in communication 59a. 
In this empirical reduced equation of state 
1) The translation of the first and second part of this article are treated as a 
whole, hence some minor changes in text will be found. 
2) Arch. Néerl., (2), 5, 644, 1900; Comm. phys. lab. Leiden, n°. 65. 
5) Thesis for the doctorate, Leiden, 1899. 
4) Proc. Royal Acad., 29 Sept. 1900, p. 275; Comm. 59a. 
6) Ibid. p. 289; Comm., n°. 595. 
6) Thesis for the doctorate, Leiden, 1892. 
7) Proc. Royal Acad., June 1901; Comm., n°. 71. 
5) Arch. Néerl., (2), 6, 874, 1901; Gomm., n°. 74, 
