275 



Physics. — "Isofhcruials of monaiomlc sjihstances and their hinary 

 mLvtures. XVI. New determination of the vapoiir-jjressares 

 of solid arc/on doivn to -205°." Coiiini. N". \AOa IVoni 

 the Physical Laboriitory at Leiden. By C. A. Crommelin. 

 (Communicated by Piof. H. Kamkrlingh Onnf.s). 



(Gomiiiunicated in the meeting of March 28, 1914). 



The vapour-pressures of solid argon, which are communicated 

 below, form an extension of and have partly to replace those published 

 on a former occasion. M 



The measurements were made in the usual vapour-pressure apparatus 

 for low temperatures.^) 



The manometer on which the pressures were read was constructed 

 after the model used by G. Holst for his measurements on ammonia 

 and methyl-chloride to be published shortly: this form of manometer 

 gives perfect security against leakage. 



The method of conducting the measurements gives no occasion 

 for special remarks : we refer the reader to the previous paper. It 

 may be mentioned however, that the temperatures were measured 

 with a gold-resistance thermometer, as below — 200^ gold is prefer- 

 able to platinum. This thermometer was very carefully compared 

 with the standard-platinum-thermometer Ptj. 



I am indebted to Mr. P. G. Cath assistant in the physical Labo- 

 ratory for the measurement and calculation of the temperatures and 

 for the comparison of the two resistance-thermometers referred to. 



Table I contains the results of the observations and the deviations 

 from the RANKiNE-BosE-formula: 



with the following values for the coefficients 



auB == 4- 6.6421 CRu =r — 0.67743 X 10^ 



6rb — — 3.7181 X 10' </ri5 = + 0.28034 X 10" 



1) G. A. Crommklin, Gomm, Leiden. N^. 138c. The measurements were repeated 

 because shortly after the publication doubt arose as to the accuracy of the determi- 

 nations at the lowest temperatures (see note on p. 23 of Gomm. N". 138c). The new 

 measurements showed this doubt to be justified, the observation at — 20G°.04 

 being found altogether wrong and the one at — 179°.62 not very accurate. The 

 remaining observations of Gomm. N^. 138c correspond well to those published 

 here. The probable cause of the errors must be air having leaked into the argon 

 at the low pressures: but I cannot explain how it is that this was not noticed 

 during the measurements. 



2) H. Kamerlingh Onnes and G. Braak, Gomm. N". 107a. 



