515 



To prevent too rapid an evaporation of tlie bath the cryostat- 

 vessel .Sj (fig. Ij is proteeled bj a tube with liqnid air. 



If the available neon is not qnite pnre and if it is still desired 

 to start the work with it without the previous purification by means 

 of the circulation under pressure over carbon cooled in liquid air, 

 it will be possible instead of the drying tube Z), to insert between 

 4 and 5 a carbon-tube D^ arranged for purification under ordinary 

 air-pressure, immersed in liquid-aii' witii a drying-apparatus preceding it. 



In the experiments the liquid gas in the bath was always ob(ained 

 in a perfectly transparent condition. Only the first quantity of 

 liquid neon which flows into the cryostat-vessel and evaporates there 

 very rapidly, left behind a little of a white substance (solid nitrogen 

 or solid air?) which dissolved again in the liquid gas which flows 

 in afterwards. A slight ring-shaped deposit was also noticed above 

 the liquid surface in the evaporation of the bath. The gas had "thus 

 not been quite pure; as a matter of fact this can hardly' be e.\pected, 

 as long as it is allowed to come into contact with the oil of the 

 gasometers. The use of the latter, however, simplifies the o|)erations 

 considerably, and the very slight impurity does not give the least 

 trouble. 



It was found that ihe (piantity of li(pii(i in the bath could be 

 made as much as 400 cc. 



I am glad to Ihaidv Mr. (t. J. Fi.im, chief instrumenlmaker in 

 !he cryogenic laboratory, once again for his help in the construction 

 of the apparatus described in this paper. 



Physics. — "Igollieiiihils of inonatoinic </(i.<i's and of' tlwir hinnnj 



mUtwes XVII. Isolhf minis of neon and preliininurt/ deter- 



niinations concernhu/ the I [(fidd condition of neon." By Prof. H. 



Kameklingh Onnes and C. A. Ckommelin. (Communication 



147(/ from the Physical Ijaboratory at Leiden). 



(Communicated in the meeting of June 2(i, 1915). 



'J. l.fotherntal.i of neon. This section contains a first instalment 



of the isothermal-determinations, by which we hope to obtain the 



equation of state of neon at low temperatures. The isothermals of 



0° C. and 20° C. have been investigated from 20 —93 and from 



20 — 84 atmospheres respectively; they give sufficient data for the 



connections which are required for the reduction of the observations 



concerning the isothermals of lower temperatures. Parts of isothermals 



for -182°.6 C, — 200°.l C, — 208.°1 C, - 21 3M C. and — 217°.5 C. 



are also given, which may serve as a first survey and even now 



