Physics. — “The influence of admixtures on the critical phenomena 
of simple substances and the explanation of Tricarer’s expe- 
riments.” By J. B. VrrscuarreLt. Supplement N°. 10 to the 
Communications from the Physical Laboratory at Leiden by 
Prof. KAMERLINGH ONNEs. 
§ 1. Introduction. That small proportions of any admixture cannot but 
have a great influence on the critical phenomena of a simple substance 
has repeatedly been demonstrated by KAMERLINGH Onnus and his pupils. 
This conviction led them to look for an explanation of the abnormal 
phenomena at the critical point — on which some observers base their 
doubts of the validity of the theories of ANprEws and VAN DER 
Waars — by preference in small quantities of admixture, and gave rise 
in the Leiden laboratory to several researches in which the greatest 
care was bestowed upon the cleaning of the substances investigated. 
As early as Oct. °98, in Comm. N°. 8, p. 15, Kuenen has demon- 
strated the importance of phenomena of retardation, due to the 
irregular distribution of admixtures. In Comm. N°. 11 (Proc. May ’94) 
he proved experimentally that, when pure substances were used, the 
deviations found by Gatirzins were not observed. The subject of 
Comm. N°. 68, p. 4 (Proc. April ’01, p. 629) was a difference in 
opinion between pr Hern and KAMeERLINGH ONNEs about the significance 
of the former’s well-known experiments, of which the results were 
ascribed by the latter to admixtures. I have taken part in some 
preliminary experiments undertaken in consequence of this difference 
of opinion. They gave us the conviction that pr HwreN'’s observations 
required systematic corrections and that, if these were applied, the — 
observations would agree with the theories of ANDREWs and VAN DER 
Waals’). 
Indeed, according to KAMERLINGH ONNkES’ opinion, maintained by 
him in Comm. N°. 68, p. 18 (Proceedings, April ‘01, p. 637), the 
deviations found should be ascribed for a good deal to impurities, and 
should be explained by means of vaN DER W aars’ theory of mixtures ’*), 
Le. p. 6 (Proc. p. 681). Moreover, if attention were paid to the 
variation of the molecular pressure the deviations to be expected in 
consequence of ,admixtures would show exactly the same nature as 
those observed by pe Heen, while the variation of the molecular pressure 
owing to impurities, however small it may be for a small quantity of 
admixture, would yet cause considerable differences of density owing 
1) A more careful repetition of those preliminary researches is begun at Leiden 
soon after the controversy wilh pe Heen. 
2)Cf. also Harrman, Suppl. N°.3 to the Comms. from the Phys. Lab. at Leiden, p. 47. 
