1898 - 99 .] Sulphuric Acid and Sulphates in Solution. 
487 
Experimental Method. 
The concentrations of the free acid, neutral sulphate and acid 
sulphate in solutions containing sulphuric acid and a neutral 
sulphate were determined by means of a reaction velocity method, 
viz., by the catalysis of ethylic acetate. The velocity with which 
a solution effects the catalysis gives a measure of the free acid 
which it contains. As the experimental method employed has 
already been described by several investigators (Ostwald, Journ. 
prald. Chem ., xxxv. 112; Arrhenius, Zeitsch. physik. Chem., 
i. 110), it is unnecessary that I should give it in detail here. 
Equal volumes of a known strength of ethylic acetate solution 
and of a solution containing sulphuric acid and a neutral sulphate 
in definite proportions, were mixed at the temperature of the 
thermostat. In order that disturbing influences should be reduced 
to a minimum, the solutions employed were made as dilute as was 
consistent with a sufficiently rapid catalysis, which would admit of 
accurate and convenient measurement at 35° ’0. It was not advis- 
able to use a higher temperature on account of the volatility of the 
ester. The mixed solutions were so prepared that they had the 
correct concentrations at the temperature of the thermostat. One 
example will suffice to indicate the procedure. 
It is wished to determine the velocity of catalysis with a solution 
containing O’ 2 equivalent normal* sulphuric acid, and 04 equiva- 
lent normal potassium sulphate. Forty c.c. normal sulphuric acid 
were mixed with 20 c.c. potassium sulphate solution of the same 
concentration, and made up to 100 c.c. at 35°. Fifty c.c. of this 
solution were then mixed with an equal volume of O' 2 normal 
ethylic acetate, which was previously heated to the temperature of 
the thermostat, and measured at that temperature. At 35°, and at 
the beginning of the reaction, the mixture was then 0*2 normal 
with respect to sulphuric acid, and 0T normal with respect to 
potassium sulphate and to ethylic acetate. It was assumed that 
the volume of the mixture was equal to 100 c.c. The concentra- 
tion of the ethylic acetate was 0*1 normal in all the experiments. 
At intervals, portions of 5 or 10 c.c. were withdrawn by means 
* All concentrations are given in gram -equivalents per litre. 
