﻿of Phosphorus, Sulphur, and Aldehyde. 533 



The constant is obtained from the condition thai .r = 0, 

 when / = 0. 



This form of the integrated equation can only be used when 

 {t(> — a) is positive, because its square root occurs in the 

 expression. For the case that excess of aldehyde is present 

 at the commencement of the experiment, and (2b — a) there- 

 fore negative, the integrated equation may be brought into the 

 following form: — 



_ 2l!m — 2—k'a. , (&—#)* , , f/1 ., /KI . 



K^= tttti — tan -1 -^ -f-i + k(b — ,i;)»- + const. . (5b) 



f a — 2b\* 



/a — 20y 

 V~2~J 



The values of K in Table "VI. are calculated by means of 

 equations (5a) and (56), and show that up to a pressure of 

 450 millim. these equations are in harmony with the experi- 

 mental results. 



When the partial pressure of the oxygen is higher than 

 about 450 millim., however, the values of K decrease. This 

 points to the existence of an upper limit of pressure, above 

 which the reaction either stops altogether or goes forward 

 with a velocity very much smaller than that which would be 

 deduced from equation 5. 



As a matter of fact, in the two last experiments given in 

 Table VI. no reaction occurred when the pressure of the 

 oxygen exceeded 530 millim. Further experiments are, how- 

 ever, needed in order to put this very interesting behaviour 

 beyond doubt. 



We mav say, therefore, that oxygen and aldehyde-vapour 

 react with formation of acetic acid with a velocity which is 

 proportional to the pressure of the aldehyde-vapour and to 

 the square root of the pressure of the oxygen. It is possible 

 that a pressure of oxygen exists above which this is no longer 

 true. At 20° this pressure appears to be that due to about 

 450 millim. of mercury. 



Interpretation of Results. 



Following van't Hoff*, the velocity of a reaction of the 

 general form 



raA + nB+ . .. =pC + qD+ .. ., 



that is of one in which m molecules of a substance A react 

 with n molecules of B, &c, to form p, q, &c. molecules of 

 the new substances C, D, &c, may be written 



_**=*. Cj.C» (6) 



* Etudes de Dynamique Chimique. 



