314 M. Hittorf on Phosphorus. 



phorus is deposited. Only after about two hours' heating is a 

 stable maximum obtained; it very slowly increases with the 

 temperature, and is always considerably greater than that dis- 

 engaged at the same temperature from red phosphorus. 



A large quantity of colourless phosphorus was heated in hy- 

 drogen gas under various pressures, which increased to four at- 

 mospheres. When heated over free flame it always boiled rapidly ; 

 the formation of vapour was always more rapid than the change 

 into red phosphorus. 



From Hittorf 'b experiments it follows that the vapour of red 

 phosphorus may be cooled from 447° to 358° (that is, through 

 90°) without changing its condition. This was confirmed by the 

 fact, that in an exhausted tube one end of which was heated to 

 358° and the other, which contained red phosphorus, to 447°, 

 no deposit of phosphorus was observed in the first. In order to 

 observe the pressures directly, phosphorus was placed in the 

 closed end of an exhausted siphon-barometer the bend of which 

 was closed by bismuth ; this metal does not combine with phos- 

 phorus at 447°, and only absorbs its vapour to a small extent. 

 The open leg was filled with hydrogen and was connected with 

 a manometer, so that, by disengagement of hydrogen and pressure 

 of mercury, pressure could be exerted on the bismuth. When 

 the siphon part was heated to 447°, the phosphorus-vapour had 

 a pressure of 1| atmosphere, much less, therefore, than 1633 

 millims., which the first experiments gave ; the difference arises 

 from the absorption of phosphorus by the bismuth. It could, 

 however, be shown that, spite of the fact that the formation of 

 vapour had ceased, the vapour had not the density which it 

 could possess at this temperature ; for the pressure of the hydro- 

 gen could be raised to 3| atmospheres before the short leg was 

 completely filled with bismuth. If the pressure was again dimi- 

 nished, a perceptible and very slow formation of vapour ensued 

 under a pressure of \\ atmosphere. 



If an exhausted tube containing red phosphorus be heated in 

 one part to 530°, and in another to 447°, microscopic needles 

 are deposited in the cooler part. These crystals were obtained 

 of a larger size by taking advantage of the property which lead 

 has of dissolving phosphorus at high temperatures and deposit- 

 ing it on cooling. Colourless phosphorus was placed with lead 

 in a strong hard glass tube, which was exhausted of air and then 

 sealed. This tube was placed in an iron one which had screw 

 plates at each end, the interstices being filled with magnesia, and 

 the whole heated in the flame of five Bunsen's burners for 8 or 10 

 hours. The phosphorus was obtained on the surface of the lead 

 as striated prismatic lamina? several lines in length and bent like 

 tulip-leaves; they had a metallic lustre, were black in reflected 



