872 



Physics. — "Investigation of the equilibrium liquid — vapour of the 

 system argon — nitrogen". By G. Holst and L. Hamburger. 

 (Communicaled by Professor H. Kamermnoh Onnes.) 



(Communicated in tlie Meeting of October 30, 1915). 



Summary: I IntroducHov. II. Preparation and analysis of the gases. 1. Pre- 

 paration. 2. Test ol purity. 3. Metliods of analysis. III. Temperature measurement. 

 IV Determination of the end-points of condensation. 1. Apparatus. 2 Vapourpressures 

 of oxygen, nitrogen and argon. 3. Mixtures. V. Determination of the ^joints of 

 beginning cond' nsation. 1. Apparatus. 2. Measurements. 3. Equation of state of 

 the mixtures. VI. Tx- and px-diagrams. VII. Resumé. 



1. Introduction. 



Owing to tlie development in recent years of tlie incandescent- 

 lamp industry tlie problem of the technical preparation of argon 

 has come to the front. For this purpose it was natural that beside 

 chemical methods the cryogenic method sliould draw the attention. 

 As it is a simple matter to obtain mixtures of argon and nitrogen 

 by chemically removing the oxygen from oxygen-nitrogen mixlurcs 

 which are rich in argon, an investigation became desirable of the 

 behaviour of argon-nitrogen mixtures at low temperature with a 

 view to collecting useful data for a possible argon-nitrogen rectification. 

 This investigation has been carried out by us and we have determ- 

 ined the composition of the liquid and vapour phase as a function 

 of tempei'ature and pressure in the corresponding range of temperatures. 



H. Preparation and analysis of the gases. 



1. Preparation. 



The preparation of the gases was in general cariied out in glass 

 apparatus which had been previously exhausted with a mercury 

 pump and liquid air to a pressure of 0.0003 to O.OOl mm. and 

 subsequently washed out with pure gas. For the calibration of our 

 thermometer the vapour-pressure of pure oxygen was used. 



a. Oxygen. 



This gas we prepared from recrystallised, dry potassium per- 

 manganate ; the first portion of the gas evolved was drawn away 

 and the rest of the oxygen formed was condensed ; the middle 

 fraction of the condensed gas was used. 



b. Nitrogen. 



This gas we prepared from ammonium sulphate, potassium 

 chromate and sodium nitrite; in the purification special attention 



