338 Messrs Jones and Richardson, Method for determining 
the following expression has been deduced for the amount of 
pyruvic hydrazone formed : 
7 = 1 + «*. ( 3 ) 
C 2 
where c 1 = 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 T 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 T 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’^ 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, T 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 b c.c. at 0° C. and 760 mm. 
Then the concentration of the hydrogen ions in the solution is 
given by 
x — 
1 (fl _ A - i ( _ _ i ') 
a\b l )-™\b 1 ) * 
1 Kohlrausch, Wied. Ann. xxvi. 161. 
