1181 



In this way the constant C is now determined. It' we calculate 



Q 



the qiiantitv - with this value of C from the ditFerent observations, 

 * ' it; 



we obtain the values given in the (>''' column of table I. From this 



follows as mean value for Q 9,96 K. Cal. 



In connection with the deviations trom the mean value 5031,4 



Q 

 which the different values ot — present (see column 7) it is to be 



expected that the above value for the heat of evaporation is pret I y 

 accurate. Finally the last column gives the calculated pressure when 



Q 

 the values for C and — heading the table are used. 



R 



To give a better graphical survey of what has been found, the 



discussed lines are once more separately represented in Fig. 3. 



Tlie upmost line again gives T hi p as function of 7'. 



§ 3. Determination of the vapour pressure line of liquid lohite 

 phosphorus. 



If the difficulties in the preceding experiments were great, because 

 many of the glass spring manometers already burst before the triple 

 point of the red phosphorus had been reached, the difficulties in the 

 following experiments were so great as to seem almost insuperable. 



It is self-evident that the determination of the vapour tension of 

 the white phosphorus at temperatures at which the conversion to 

 solid red phosphorus still proceeds slowly, is attended with few diffi- 

 culties. 



Up to 312° this line had already been determined by Jolibois ^) 

 with pretty great accuracy. 



For the purpose we had in view, it was, however, necessary to 

 carry these experiments up to as high temperatures as possible. In 

 this we meet, however, with different difficulties. In the first place 

 the molten white phosphorus begins rapidly to convert into the solid 

 red modification from =t 280° on rise of temperature, in consequence 

 of which the liquid phase has disappeared in a comparatively short 

 time, and the prevailing vapour tension, thei'efore, no longer corre- 

 sponds with the vapour tension of the liquid phase at that temperature. 



Hence to find points of the vapour pressure line of the liquid 

 white phosphorus at higher temperatures, one has to heat the glass 

 spring manometer as quickly as possible to a definite temperature, 

 and then to keep the temperature constant for some time. 



1) Theses, Paris 1910. 



