( 235 ) 



FiK. S. 



the second iuoUkmI foi- tempoi";ilui-es bclow — 43° (inelting-j)()int of 

 mercni-y). When wc iiuide a first trial in tiiis direclion, a higiidegree 

 of accnracv was not aimed at. In order lo answer several questions 

 the accuracy we have reached is sufllicioul and for the calcidalinu 

 of corrections for more accurate deterniinalions i( is quite suflicient. 



In our measurements we have used the 

 apparatus which is represented schematically 

 in tig. 3. It is in |)rinciple a twice heul tul)e 

 of Cailletkt, of which one end is immersed 

 in the cryostat of the temperature 7' and 

 filled with a known (pianllty of a mixture 

 of known composition .r, which by forcing 

 uj) mercury a( the ordinary (or higher) 

 temperature T" is brought to condensation 

 at T. 



The mixture of which the ((uauliiy and the composition ,/,• are 

 known, is then only partly contained in the vessel 7' at the tem- 

 perature of investigation. Another part is necessarily in a tube at 

 the ordinary or higher temperature 7'" which is connected with the 

 vessel by means of a capillary tube. This involves complications, 

 not with regard to the measurement of the begin condensation 

 pressure l)^,x for the composition .r; for until the condensation of tiie 

 first traces of liquid, with respect to which the vapour is a phase 

 of equilibrium, the composition of the vapour phase in the space at 

 low temperature remains as it was originally, aiul hence the com- 

 position of the vapour phase of ecjuilibrium is perfectly known; but 

 with regard to the determination of the end condensation pressure 

 ptjc of the mixture with the composition .r. For we cannot condense 

 the whole quantity of the mixture at low teuq)erature. Ileiu-e 

 the composition of the liipiid phase at T, al)ove which there is a 

 vapour phase of a com[)ositiou diiVei-ing in the main fi-om this or 

 the original composition, is no longer indicated by the latter and 

 therefore unknown. 



We can, howexci-, liud this composition by ap|)lying a correction 

 to the original couqwsitiou ./; which, as long as the vapour phase 

 occupies only a small volume and remains under a moderate pressure, 

 is not very large (com p. § 5). 



§ 2. General iirramjement of the incdsi/reniciifs. 

 A schemalical re[)resentation of it will be found on PI. I, fig. 1. 

 The letters are the same as those used on the plates to which we 

 shall refer. 



The \()biiu('uouioler A' ^with manometer A/, comp. Comni. N". 84, 



16 



Piüceediugs Royal Acad. Amsterdam. Vol. Vii. 



