1 1 7.S 



ilial for every determination the temperature was raised above tiie 

 tri[)le point, and then was lowered as cpiickly as possible to a 

 definite temperature, which was then kept constant for some time, 

 till the vapour tension had become constant. Thus a constant vapour 

 tension could be observed even at the lowest point ± 504° during 

 5 minutes. On continuation of the experiment pretty suddenly a 

 decrease set in, which pointed to this that at that moment the liquid 

 phase had disappeared, and had been entirely converted to the solid 

 red phosphorus. 



That these vapour tensions under the triple point really refer to 

 the saturate vapour could be proved by this that when after the 

 determination of the vapour tension at 550°. the temperature was 

 not tirst raised above the triple point temperature, but at once to 

 562°, a vai)Our tension was observed at this latter temperature, which 

 fitted exactly in the found vapour pressure line. After this deter- 

 mination at 562° we heated at once to 574°, and also the vapour 

 tension observed at this temperature lay on the line already found. 



It follows, therefore, from this that the vapour at 502° and 574° 

 was still saturated with the vapour of the liquid red phosphorus, so 

 that it is perfectly sure that this must also have been the case just 

 before and at the lower temperature 550°. 



The results of the vapour tension determinations of the liquid red 

 phosphorus are given in the sulijoined table. In the fii'St column one 

 (inds the number of the numometer, and in the second column the 

 temperature, the third giN'ing the pressure in atmospheres. 



In the PT representation Fig. 2 these results are graphically 

 represented by the line end, from which follows that the different 

 observations yield a very regular curve. Only the last |)oint at 512° 

 lies too low. 



The point n is the point where the vapour pressure line of the 

 solid red phosphorus mn (more about this later) intersects the vapour 

 pressure line of the liquid red phosphorus, so the trij)le point of 

 the red phosphorus. 



When the saturation heat is no temperature function, the vapour 

 pressure formula 



dln'p _ Q 

 dT RT ^ ' 



on integration yields the expression : 



lnp = -^^+C (2) 



or 



