694 Research Staff of the G. E. C, London, on the 



The yellow substance does not disappear from the walls if 

 the lamp is exhausted for many hours to a very high vacuum 

 through a liquid- air trap. If oxygen is admitted to the 

 vessel, it is not absorbed at room temperature. The yellow 

 substance is not therefore, as seems to have sometimes been 

 believed, white or "yellow" phosphorus. It is almost 

 certainly red phosphorus or some modification with similar 

 properties. If the lamp is baked to 650° K. or more, the 

 yellow coloration disappears gradually ; some of it merely 

 distils to the cooler connecting tubes, but some collects in 

 the liquid-air trap as white phosphorus, which will absorb 

 oxygen at room temperatures. If a little oxygen is admitted 

 during baking, it is absorbed when the temperature reaches 

 650° K. These observations are completely accordant with 

 the view that the yellow substance is red phosphorus, 

 deposited on the walls in an extremely fine film. The 

 discharge converts the white vapour into the red solid ; the 

 change is one of those chemical actions (see § 11) we should 

 expect to be brought about by the discharge. 



Accordingly, the disappearance of phosphorus vapour 

 under the discharge does not seem to differ essentially from 

 that of the other gases that have been noticed. In all cases 

 the gas that has disappeared is deposited on the w 7 alls ; in 

 phosphorus, as in CO, this deposition is aided by a chemical 

 change in the gas which makes it adhere more readily to the 

 walls. Nevertheless, these are important peculiarities about 

 phosphorus. The first is that the product of the chemical 

 change is a stable solid body which has no appreciable 

 vapour-pressure even when it is not adhering to glass* ; no 

 evidence of the formation of such stable solids has been 

 found in the other gases. 



* An attempt was made to determine the vapour-pressure of red phos- 

 phorus by the method just mentioned ; but the only result that could be 

 obtained was that the vapour-pressure at room temperature is less, and 

 probably much less, than 0*001 mm. The glow potential of red phospho- 

 rus vapour, whether introduced as a powder or deposited on the walls by 

 the discharge through white phosphorus vapour, is certainly greater than 

 600 volts — a result which indicates again that the vapour-pressure must 

 be very small. 



In the earlier work some very puzzling indications were obtained of a 

 residual vapour-pressure of the substance deposited on the walls 

 amounting to - 0009 mm., giving a glow potential as low as 32*5 volts. 

 It is now believed that this vapour was that of oxides (or possibly other 

 compounds) of phosphorus, formed by the reaction of the phosphorus 

 vapour with carbon monoxide under the influence of the discharge. But 

 as it has been found so far impossible to reproduce these early experi- 

 ments, the matter has not been cleared up satisfactorily. However, no 

 doubt is now entertained that the vapour-pressure of red phosphorus is 

 inappreciable for these experiments. 



