<v 
chemical change by measurement of the gases evolved. 591 
If these values for the logarithm of the constant K are plotted 
with the temperature, points lying very nearly on a straight line 
are obtained, and it may be calculated that the rate of reaction is 
increased 3'59 times by a rise in temperature of 10 degrees. 
By interpolation the value for the constant at 50° is found to 
be ‘0424, and this number is inserted in the above table. 
The experiments of Cain and Nicoll, in which no attempt was 
made to remove the nitrogen with which the solution was super- 
saturated, led to values of K considerably lower than these, the 
constant at 50° being '0298 and at 60° T09. In many of the 
experiments there were greater variations in the values of 
the velocity constants than justify the conclusion that the action 
is unimolecular, even throughout the ranges from which obser- 
vations were selected for calculation. This is only what might 
be expected in view of the fact that the rate of evolution of 
gas from the still solution depends only indirectly on the rate 
of its liberation from the decomposing diazo compound, being 
greatly influenced by the rate of evolution of the particular gas 
from its supersaturated solution. 
The Decomposition of Formic Acid by Sulphuric Acid. 
The reaction between formic acid and sulphuric acid was 
among those studied by Veley, Phil. Trans. 1888, p. 257. 
He found that the action was bimolecular, and that when 
silica, pumice, etc. were added to the solution, the rate of evolution 
of gas was much increased, though the action remained bimolecular. 
In neither case was the solution agitated in any way. 
To investigate this action the apparatus used was the same as 
that in the case of diazobenzene chloride, except that a stirrer, 
driven by a separate motor, was used to keep the water in the 
bath in constant motion. 
The reaction-vessel was rinsed out several times with pure 
concentrated sulphuric acid. The air was then pumped out of 
the vessel, and pure carbon monoxide allowed to enter, and this 
process was repeated a second time. By this means air was 
removed from the vessel, and any possibility of action between 
formic acid and the oxygen of the air was avoided. The vessel 
was then placed in the water-bath, which was kept at a constant 
temperature of 72° C. 
A reaction mixture was prepared by slowly adding 5 c.c. of an 
IV/ 2 solution of sodium formate to 20 c.c. pure sulphuric acid, 
and cooling during the addition, so that the temperature of the 
solution just rose to that of the water-bath. Thus no time was 
lost in heating up the solution to the required temperature, and 
very little decomposition had taken place before the solution 
was introduced into the vessel. 
