258 MB. V. H. VELBY ON THE CONDITIONS OF THE 



of experiments on the rate of formation of gases from liquids. For convenience, the 

 paper will be divided into three parts. In Part I. the effect produced by the presence 

 of finely divided particles is investigated ; in Part II. the result of variation of pressure 

 is studied ; in Part III. the particular case of the decomposition of formic acid into 

 carbonic oxide and water, under the influence of concentrated sulphuric acid, is 

 investigated, the only conditions varied being those of temperature and mass. The 

 mathematical representation of this change is also discussed, and the results observed 

 are compared with those calculated according to the hypothesis adopted. 



Before passing on to details, I should wish at once to state that these investigations 

 were commenced at the instigation of Mr. HAKCOURT, who was kind enough to devise 

 for me the various apparatus herein described, and without whose constant co-operation 

 and advice this research could not have been completed. The experiments were con- 

 ducted in the laboratory of Christ Church, Oxford. 



II. Previous Experiments on the Evolution of Gases from Liquids in ivhich they 



are formed. 



The principal chemical changes of this nature, at present investigated, are the 

 decomposition of ammonium nitrate into nitrous oxide and steam, of potassium 

 chlorate into potassium chloride and oxygen, and of hydrogen peroxide into water 

 and oxygen. 



The first of these changes has been studied from the thermo-chemical side by 

 BERTHELOT,* and from a chemical point of view by myself, t BERTHELOT concludes 

 from his experiments that ammonium nitrate, when heated to 200 C., is decomposed 

 initially into ammonia and nitric acid, which in some degree distil in the gaseous 

 form, recombining in the cooler parts of the apparatus to reproduce the original salt, 

 but to a greater degree react together to form nitrous oxide and steam. These 

 changes are represented as follows : 



(i.) NH 4 N0 3 = NH 3 + HN0 3 . 

 (ii.) NH 3 + HN0 3 = N 2 O +2H 2 O. 



My investigations established that the rate of the second change is conditioned by 

 the extent of the first : that is to say, the rate of formation of nitrous oxide, taken 

 as the measure of the decomposition, depends upon the proportion either of ammonia 

 or of nitric acid present in excess over the quantities of base and acid required for 

 their complete neutralisation. Thus, an excess of ammonia, other conditions remaining 

 the same, retarded, or even completely stopped, the decomposition, and an excess of 

 nitric acid produced the same effect, though to a less marked degree. Unpublished 



* ' Annales de Chimie,' [4], vol. 18, pp. 68-82, and [5], vol. 10, pp. 362-365. 

 t ' Chem. Soc. Journ.,' 1883, pp. 370-383. 



