﻿of Phosphorus, Sulphur, and Aldehyde. 535 



C (0) that of the atoms, k is a constant which depends on the 

 temperature*. As the heat of formation of the oxygen 

 molecule from its atoms is probably positive, the equilibrium 

 will change with falling temperature, in such a way that the 

 concentration of the oxygen atoms will diminish. It will, 

 however, probably never become nothing. If this be true at 

 ordinary temperatures, we shall have 



C (0) = const. s/0^ tY 



As the concentration of the oxygen atoms is small, we can put 

 the concentration of the oxygen molecules proportional to the 

 pressure of the gas, and the concentration of the oxygen atoms 

 will then be proportional to the square root of the pressure of 

 oxygen. If we assume, therefore, that the atoms alone take 

 part in the oxidation of the aldehyde, we shall have the 

 velocity of the reaction always proportional to the square 

 root of the pressure of the oxygen. 



Although the results of the experiments with aldehyde admit 

 of such a simple interpretation, it is doubtful whether this is 

 also the case with those obtained with phosphorus and sulphur. 



We should expect the connexion between the velocity of 

 the reaction and the concentration of the oxygen to be less 

 simple than that actually found. 



Possibly in the case of sulphur and phosphorus with dry 

 oxygen the reaction takes place in stages ; for example, 



p i+ o=p i ot. 



The velocity of the whole reaction would then be the sum of 

 the velocities of the part reactions, each one of which would 

 be proportional to the concentration of the oxygen atoms. 

 This view is also in agreement with the fact that when phos- 

 phorus is burnt with a limited supply of oxygen, the lower 

 oxides, such as P 4 6 , are formed. 



The fact that the presence of moisture accelerates the oxi- 

 dation of phosphorusj and sulphur is also in accordance with 

 the view that the oxidation is due to the presence of oxygen 

 atoms ; for Professor J. J. Thomson § has found that it is 



* See van't Hoff, Etudes, p. 127. _ 



t The existence of this oxide, discovered by Le Verrier, is rendered 

 probable by the work of Reinizer and Goldschmidt (Berl. Ber. xiii. p. 845, 

 1880). 



% In very drv oxygen phosphorus apparently does not oxidize at all. 

 (H. 13. Baker, Phil. Trans. 1888, p. 571.) Unfortunately Baker does not 

 mention particularly the pressure under which the oxygen stood. Sulphur 

 still burns in extremely dry oxygen, but with much greater difficulty 

 than when the gas is moist. (Baker j and also Dewar, Proc. Roy. Soc. 

 January 1893.) 



§ J. J. Thomson, British Association, Oxford Meeting, 1894. 



