338 Messrs Jones and Richardson, Method for determining 



the following expression has been deduced for the amount of 

 pyruvic hydrazone formed : 



- = 1 + ax, (3) 



where Cj = original concentration of oxalacetic hydrazone, 



c 2 = final concentration of pyruvic hydrazone, 



x = concentration of hydrogen ions, 



and a is a constant which is equal to the velocity constant of the 



reaction (2) divided by the product of the velocity constant of the 



reaction (1) into the dissociation constant of oxalacetic hydrazone. 



The amount of carbon dioxide produced can be readily expressed 



in terms of the final concentration of the pyruvic hydrazone to 



which it is proportional. On theoretical grounds it was to be 



expected that with a solution of '1 gram of the hydrazone in 



100 c.c. the ionisation of the substance could be neglected compared 



N 

 with that due to ^. sulphuric acid, and as a matter of fact the 



experiments show that this holds with solutions stronger than one- 

 fiftieth normal. 



In the experiments the amount of carbon dioxide produced 

 when # 1 gram of the hydrazone was heated with 100 c.c. of acid of 

 various strengths was estimated by absorption in baryta and 

 titration of the excess. The results obtained, as shown in the 

 following table, fully confirm the theoretical conclusions. 



The values in column (4) were calculated from Kohlrausch's 1 

 measurements at 18°, whereas the values for -ax are proportional 

 to the concentration at 100°. This may explain the slight varia- 

 tion in the values of the constant a near the top of column (5) : 

 the gradual increase towards the bottom being due to the increas- 

 ing effect of the ionisation of the hydrazone itself in the more 

 dilute solutions. 



This reaction affords a simple, quick and easy method of 

 measuring the concentration of hydrogen ions in solution and 

 therefore of determining the dissociation constants of acids. To 

 determine the concentration of the hydrogen ions in a given acid 

 solution, "1 gram of oxalacetic hydrazone is heated with 100 c.c. 

 of the solution to 100°C and the amount of carbon dioxide 

 evolved is estimated. Let this be 6 c.c. at 0° C. and 760 mm. 

 Then the concentration of the hydrogen ions in the solution is 

 given by 



x = 



alb L * U 



1 Kohlrausch, Wied. Ann. xxvi. 161. 



