﻿of Phosphorus, Sulphur, and Aldehyde. 



523 



It was found that more satisfactory results could bo ob- 

 tained by using a different method, in which the pressure was 

 kept constant and the diminution of volume measured. This 

 method has the advantage that it allows several measure- 

 ments of the velocity to be made at each pressure ; by this 

 means accidental variations can be eliminated. It was noticed, 

 for example, almost invariably that at the beginning of an 

 experiment (the pressure being constant) the rate at which 

 the volume diminished was not constant. The reaction com- 

 menced too fast, and only reached a constant velocity after 

 some time. This doubtless accounts for the abnormally 

 large value of K t at the beginning of the experiment in 

 Table IV. 



The apparatus finally adopted is shown in fig. 5. 



Fig. 5. 



The tube S containing the sulphur and oxygen remains 

 unchanged. It was attached to a graduated tube A, con- 

 taining mercury, the height of which could be changed by 

 means of the reservoir B. C is a three-way tap ; D a 

 sensitive gauge containing bromnaphthalene, it serves to show 

 when the pressure in the part of the apparatus to its left is 

 equal to that in the reservoir F. The tap E serves to put the 

 parts of the apparatus to the right and to the left of D in 

 communication with each other when necessary. The reservoir 

 F, which serves to keep the pressure constant, is in com- 

 munication with the manometer G and with an air-pump. 



2N2 



