272 



MB. V. H. VELEY ON THE CONDITIONS OF THE 



These results show that, while the evolution of oxygen from the potassium chlorate 

 and manganese peroxide mixture is very rapid while the salt still remained unfused 

 that from the potassium chlorate and barium sulphate is exceedingly small under 

 the same conditions. 



The results of the various experiments detailed above all point to the one conclu- 

 sion, that the rate of evolution of a gas formed by chemical change in an homogeneous 

 liquid is accelerated by the presence of finely divided particles which are chemically 

 inert. Thus, whether the gas is evolved from an aqueous solution or a salt in a 

 state of fusion, whether the gas is soluble in the liquid from which it is being 

 evolved or not, whether the chemical change from which the gas results takes 

 place at a temperature of 37 or 350, whether the finely divided substance is 

 porous or not, the result is uniformly the same. 



v 



PAET II. 



PHENOMENON OF INITIAL ACCELERATION AND EFFECT OF REDUCTION OF PRESSURE 



ON THE RATE OF EVOLUTION OF GASES. 



Before proceeding to discuss the effects produced by reduction of pressure on the 

 rate of evolution of gases from homogeneous liquids, it is desirable to call attention to 

 the phenomenon of initial acceleration. It was observed by Mr. HARCOUKT some 

 years ago, and confirmed by my experiments on the decomposition of ammonium 

 nitrate and on other chemical reactions detailed in the present communication, that 



