278 MR. V. H. VELEY ON THE CONDITIONS OP THE 



small quantity of the gases being lost between the last observation of I. and the first 

 of II. in the interval of time during which the collecting tube was re-filled with 

 mercury. 



Decomposition of Nitric Acid into Nitric Oxide and Water by means of 



Ferrous Sulphate. 



In the formation of nitric oxide by heating together solutions of ferrous sulphate 

 and potassium nitrate with dilute sulphuric acid, this initial acceleration was not 

 observed under the conditions of the experiments. But when the pale green liquid 

 was warmed at about 40, it gradually became darker by the solution therein of the 

 nitric oxide, a process which lasted often for half an hour or more. When the liquid 

 had become almost black, then, owing to some indeterminate cause, there was a 

 sudden outburst of gas, accompanied by an evolution of heat, the thermometer rising 

 one to two degrees. From this point the evolution of gas gradually decreased, at a 

 rate probably proportional to the diminution of mass. 



Decomposition of Ammonium Nitrite in Aqueous Solution into Nitrogen and Water. 



In the few experiments made in the course of the present investigation on the 

 above chemical change the phenomenon of initial acceleration was not observed, but 

 Mr. HABCOUBT has informed me that in his previous investigations, on a more extended 

 scale, he always observed the phenomenon, and showed that it could be reproduced 

 by temporary cooling of the liquid, as noted above in the case of the decomposition of 

 formic acid. 



Production of Hydrogen from Zinc and Sulphuric Acid. 

 Zn + H 2 S0 4 = ZnS0 4 + H 2 . 



Though the results obtained in measuring the rate of evolution of hydrogen from 

 zinc and sulphuric acid are not strictly comparable with the evolution of gas from a 

 homogeneous liquid, yet, as SPBING and AUBIN* have recently called attention in this 

 case also to an initial acceleration, which they call the " period of induction," it may 

 here be briefly considered. 



In the present research, this phenomenon was observed in the course of experiments 

 made before the publication of SPBING and AUBIN'S paper. It is probably conditioned 

 by the mechanical adherence of bubbles of gas to the surface of the metal, which is 

 always apparent when sulphuric acid comes in contact with a regular surface of the 

 metal If these bubbles are removed as fast as they are formed, or if the metal is 

 continuously rolled about within the acid liquid, no such initial acceleration can be 

 observed. 



' Annales de Chimie' [6], vol. 11, pp. 505-554. 



