240 Evolution of Gases from Homogeneous Liquids. [May 31 



produces no permanent effect on the rate of evolution of a gas from a 

 liquid, a decrease of pressure, however, produces temporarily an in- 

 crease in the rate, and an increase of pressure conversely produces 

 temporarily a decrease in the rate. 



Part III. — The case of the decomposition of formic acid into 

 carbonic oxide and water by diluted sulphuric acid is studied with 

 the aid of an apparatus by means of which the temperature is kept 

 constant within one-twentieth of a degree. It is shown that the rate 

 of evolution of carbonic oxide is expressible by the following equa- 

 tion : — 



log (t + t) + log r = log c, 



in which t is the time from the commencement of the observations ; 

 t is the interval of time from the moment of commencement, and 

 that at which, conditions remaining the same, the interval of time 

 required for unit change would have been nil ; r is the mass at the 

 end of each observation, and c is a constant. The results calculated 

 by this hypothesis agree with those observed, whether the interval of 

 time required for unit change is 30 or 960 minutes. The curve 

 expressing the rate of chemical change in terms of mass is thus 

 hyperbolic and illustrative of the law 



dr _ r 2 



which expresses the rate at which equivalent masses act upon another ; 

 1/c in each experiment is the amount of each unit mass which reacts 

 with the other per unit of time, when an unit mass of each substance 

 is present. Since then equivalent masses take part in the change, it is 

 reasonable to suppose that at first an anhydride of formic acid is 

 produced thus : — 



^0} + HCO| = HCOJ + H2a 



The anhydride is unstable, and is subsequently decomposed into 

 carbonic oxide and water, 



HCo}° = 2CO + OH s- 



The change may thus be compared to the production of ethyl 

 formate from formic acid and alcohol, 



HCO 

 H 



}0 + C ^}0 = HC0} + H30 . 



with which it shows several points of analogy. 



In the original paper the methods of observation and the apparatus 

 used are described in full, and the results obtained are set forth in a 

 series of tables. 



