J17fi 



Then a gauged theriiin-element and a ganged very sensitive resist- 

 ance tbermometer were placed in the bath for the temperature 

 measurement, so that the temperature could be measured in two 

 different ways. The bath was surrounded by a wider asbestos twlindre, 

 burners placed under it ensuring a uniform heating. 



In the determination of the vapour pressure line of the liquid red 

 phosphorus the bath was slowly raised to a temperature above the 

 melting point of this modification. 



In order to bring the needle of the glass spring manometer to its 

 zero position, the pressure in tiie space round this manometer had 

 to be continually increased. At first this was effected by slowly 

 admitting air through K^, A', and A", being open, bnt afterwards 

 this was obtained by filling the tube between the valve V and the 

 cock K^ with CO, of higher pressure, after K^ had been closed, and 

 then carefully opening the cock K^. As the open manometer could 

 indicate at most an excess of pressure of ± 4 atmospheres, K^ was 

 closed when this pressure had been reached, so that at higher 

 pressure only the closed air manometer J/., was used. In its turn 

 the airmanometer was closed at pressures of about 10 atmospheres, 

 and the metal manometer J/3 was read. It had appeared in prelimi- 

 nary experiments that the three different manometers corresponded 

 with each other very satisfactorily. 



When the red phosphorus was melted, the temperature was kept 

 constant for some time, the needle \vas brought exactly to its zero 

 position, and the pressuie was read on the air manometer. Then 

 the temperature was slightly raised or lowered ; then again put at 

 the same point, and the preceding operation was repeated to get 

 an idea of the accuracy of the method. The i-esult was that the 

 error at these high temperatures and pressures amounted to less 

 than 0,1 atm. 



In this way we could determine the vapour pressure line of the 

 molten red phosphorus up to a temperature of 634°, and a pressure 

 of 58.6 atm., which may, indeed, be called a surprising result, for 

 that a glass tube of a diameter of 2 cm. and a thickness of wall 

 of 2 mm. can resist a pressure of 58 atmospheres at a temperature 

 of 634°, was not expected by us, and in these experiments we were 

 fully prepared for a violent explosion, which, however, fortunately 

 did not take place. That the glass had not even been deformed was 

 proved by this that when the experiment was over, the zero position 

 appeared to have hardly changed. 



We have been able to continue these vapour tension determina- 

 tions of the liquid red phosphorus up to ± 85° below the triple 



