oc 
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temperature one has to take the (practically) constant velocity, which, 
when the experiment is rightly performed, sets in after a short period. 
5. The thus studied velocity shows also in absence of (lasting) 
noxious influences, an optimum for a certain temperature, which is 
contrary to the theory of Ducnavux-BLackMaNn for the explanation 
of the occurrence of a temperature optimum at physiological experi- 
ments, this theory should hence be rejected. 
6. The diffusion through the wall of the yeast cetls is no limiting 
factor in the processes studied by us. 
7. The fact that also physteo-chemical reactions deviate from the 
rule of Van ’r Horr cannot be opposed to our conclusion that, in 
the ease of the alcohol fermentation, the considerable deviation from 
that rule beneath noxious temperatures is in contradiction with the 
theory of Ductaux-BLACKMAN. 
8. On the contrary, it speaks greatly in favour of our observations 
and conclusions that the catalysis of hydro-oxygen-mixtures by colloidal 
platinum (which process presents also in other respects much analogy 
to physiological katabolisms) shows a temperature optimum in absence 
of (lasting) noxious action, so on exclusion of the time factor, and 
behaves with respect to the temperature perfectly in the same way 
as was found by us for the alcohol fermentation and the inversion 
of cane sugar by yeast invertase. 
Delft, October 1910. 
Physics. — ‘‘J/sotherms of monatomic gases and of their binary 
mirtures. VI. Coexisting liquid and vapour densities of argon ; 
calculation of the critical density of argon.” By C. A. CROMMELIN. 
Comm. N°. 118* from the Physical Laboratory at Leiden. 
(Communicated by Prof. H. KAMERLINGH ONNEs.) 
(Communicated in the meeting of September 24, 1910). 
§ 1. The experiments published a short time ago') by which the 
vapour pressures of argon above — 140° C. were determined afford 
a means of deriving the difference between the coexisting liquid and 
vapour densities at the same temperatures as those at which the 
vapour pressures were measured. As was mentioned in § 2 and 3 
of the paper just referred to, both the position of the argon meniscus 
in the low temperature reservoir and that of the mercury meniscus 
- 
1) These Proceedings May 1910. Comm. Phys. Lab. Leiden, N°. 115. For short, 
this paper which is frequently quoted in the text will be called Co:nm. 115, 
