312 M. Hittorf on Phosphorus. 



vapours at different pressures, by which other temperatures were 

 obtained. This mode of heating has two advantages over the 

 use of liquids in producing high temperatures : in the first place, 

 the temperatures are quite uniform, and may be retained for any 

 length of time; in the second, the interior of the exhausted 

 tube is visible, and that, too, in the case of strongly-coloured 

 vapours, such as that of sulphur, provided a flame is held behind 

 the tube. 



Red phosphorus, at temperatures of 307° and 324°, became 

 somewhat darker, without any other change; bat when heated 

 in the vapour of chloride of mercury (358° C), a few drops of 

 colourless phosphorus were found in the upper part of the tube, 

 the quantity of which did not increase, provided this tempera- 

 ture was not exceeded. When, however, the vapour of sulphur 

 or of sulphide of phosphorus was used, the quantity of colour- 

 less phosphorus materially increased. While the glass tube is 

 heated, this quantity of colourless phosphorus fills the interior 

 of the exhausted tube as vapour ; in a given space at a given 

 temperature, a definite quantity of vapour is formed from the 

 red phosphorus without the latter becoming liquid. When this 

 maximum of density and tension is attained, the rest of the 

 phosphorus remains unchanged. On cooling, this vapour con- 

 denses as colourless phosphorus. If the quantity of this colour- 

 less phosphorus which is formed at a given temperature in a 

 small tube of known capacity is determined, its maximum den- 

 sity is obtained. As the vapour of phosphorus is sixty-two times 

 as heavy as hydrogen at the same temperature and under the 

 same pressure, the maximum tension is obtained from the den- 

 sity found, assuming that Boyle and Gay-Lussac's law holds 

 good. In this way tension of phosphorus-vapour is obtained for 

 the following temperatures : — 



Temperatures. 



388 

 409 



447 

 530 



The last result is a little too high. 



Schrotter adduces 260° C. as the temperature at which red 

 phosphorus changes into colourless phosphorus. Hittorf found 

 that no change took place even with four hours' heating at 255°; 

 nor did oxygen combine with it at this temperature. Under 

 260° reel phosphorus is not volatile, and from that temperature 

 it gives vapours with continually increasing density and tension. 



Weight of a litre 



Tension in 



of the vapour. 



millimetres 



grm. 



0-0996 



31-5 



1-0850 



370-6 



4-538 



1636-5 



15-625 



6139 



