NAKFORE 
217, 
THURSDAY, JANUARY 7, 1904. 
THE CRITICAL STATE. 
Le Point critique des Corps purs. Pp. 
(Paris: C. Naud, 1904.) 
F late numerous attacks have been made on the 
commonly accepted theories relating to the con- 
ditions which obtain at the critical temperature of 
pure substances, and though the assailants may have 
received little support, or even attention, from the mass 
Vul + 255- 
of their physical brethren, it is time that certain | 
questions relating to the critical state were more de- | 
finitely settled. 
In the opening chapter of this work the author dis- 
‘cusses the general case of the evaporation of liquids 
at temperatures up to their critical point, leading up 
to the statement, which opens the second chapter, that 
the theories of Andrews and Van der Waals are in- 
sufficient to explain the observed phenomena. For 
instance, Battelli has attempted to prove that the 
temperature at which the meniscus disappears in a 
sealed tube containing alcohol is a function of the 
concentration of the alcohol in the tube. The experi- 
mental results are quoted; they are as follows :— 
Date of Mean density of liquid and Observed critical 
experiment vapour in sealed tube temperature 
1891 0 3195 236°39 
1892 0°3434 237 02 
1891 0°3448 236°26 
1891 0°3839 235 66 
1891 0°3889 23594 
18g2 04000 236°43 
Similar results were obtained in the case of ether, 
but it is difficult to see how they may be fairly in- 
terpreted as supporting the author’s views. <A very 
small quantity of impurity would be quite sufficient 
to account for these abnormal, but by no means con- 
cordant results. 
The experiments of Galitzin are next quoted to 
prove that the temperature of disappearance and re- 
appearance of the meniscus is dependent not only on 
the mean density of the substance in the tube, but also 
on the dimensions of the latter. Sealed tubes con- 
taining ether were heated slowly to 200° C., main- 
tained at that temperature for twenty minutes, and 
then allowed to cool slowly. A maximum difference 
of o0.g° C. between the temperatures at which the 
meniscus disappeared and reappeared again was 
observed, and as no evidence to the contrary is forth- 
coming, there is no reason for assuming that the 
temperature difference is not due to the lagging of 
the temperature of the liquid in the capillary tube after 
that of the bath. It is further remarked that, if one 
repeatedly heats and cools such a tube, the meniscus 
tends to reappear after each operation at a lower point 
in the tube. That this is not observed when the tube 
is shaken is highly significant. 
In the succeeding chapters the various methods 
which have been applied to the determination of the 
critical constants are described and criticised, theo- 
retical questions being discussed as they occur. Open- 
ing with an account of Andrews’s experiments, and 
NO 1784, VOL. 69] 
the development of his method at the hands of 
| Ramsay, Young, and others, the author leads up to 
| a discussion on the application of the modified gas 
equation to the calculation of the critical constants 
from the data for the isothermals. As an example, he 
takes Sarrau’s attempt to employ Clausius’s equation 
to calculate the critical constants of hydrogen from 
Amagat’s determinations of the compressibility of that 
gas. The results are, of course, wide of the mark, 
but it is interesting to note that Wroblewski, who in- 
vestigated the isothermals of hydrogen between 
+100° C, and —182° C., obtained, by means of a 
similar equation, a very fair approximation of their 
values. 
In chapter vi. the author discusses the effect of the 
gravity of the substance under investigation on the 
density at different levels in the capillary tube. Here 
again our knowledge of the subject is very scanty, 
dnd experimental evidence is required to support the 
theoretical results of Gouy and others who 
treated the subject mathematically. 
Particularly interesting accounts of special series 
of researches are given in the succeeding chapters. 
Olszewski’s determination of the critical-pressure of 
ethylene, oxygen, and hydrogen is described in detail, 
and the theory of the method, which is not dealt with 
in the original paper, is explained by means of a 
diagram. This piece of work is important, as it in- 
volves a new method for the determination of critical 
pressures, and gives us the only published experi- 
mental data for the critical pressure of hydrogen. 
Some of the methods described by the author as 
“ élégantes mais pur précises ’’ are interesting, as they 
furnish suggestions which may be applied to other 
problems. The behaviour of mixtures, which could not 
be entirely omitted from the work, is briefly discussed, 
and diagrams are given illustrating the graphical 
method of treating the results. A table of critical 
constants occupies several pages. : 
The final section of the book deals with the theories 
which have been put forward to account for the 
apparent irregularities in the behaviour of pure sub- 
stances, and the deviation from the simple laws hither- 
to supposed to govern the phenomena which take place 
at the critical point. The existence of two kinds of 
molecules, gasogenic and liquidogenic, which persist 
in the vapour phase, was first suggested by de Heen, 
and has recently received support from Traube and 
others. As was long ago pointed out by Sir G. Stokes, 
de Heen’s theory demands that the pressure of a 
saturated vapour of a pure substance, like that of a 
mixture, must be dependent on the relative masses of 
the liquid and vapour phases, and this is contrary to 
all experience. Modifications of this theory, involving 
an idea of a definite equilibrium dependent only on 
temperature between the two kinds of molecules, may 
be more easily tenable; but, as the author suggests, 
the existence of liquidogenic molecules, having only a 
transitory existence in the vapour phase, and dis- 
sociating slowly into gasogenic molecules, would 
account for most of the phenomena which have been 
observed. 
There are two obvious sources of error in measure- 
L 
have 
