1888.] Evolution of Gases from Homogeneous Liquids. 239 



forming greys by rotation were measnred, and the results tabulated 

 in percentages of the spectrum of white light and on a wave-length 

 scale. 



III. :i The Conditions of the Evolution of Gases from Homo- 

 geneous Liquids." By V. H. Veley, M.A., University 

 College, Oxford. Communicated by A, VERXOX Harcourt, 

 M.A., F.R.S. Received May 5, 1888. 



(Abstract.) 



This paper is conveniently divided into three parts. In part (i) an 

 account is given of the effect of finely divided particles on the rate of 

 evolution of gases resulting from chemical changes ; in part (ii) the 

 phenomenon of initial acceleration, as also the effect of variation of 

 pressure on the evolution of gases, is discussed ; in part (iii) the case 

 of the decomposition of formic acid into carbonic oxide and water is 

 investigated under constant conditions, other than those of the mass 

 of reacting substances and of temperature. 



Part I. — It is found that the addition of finely divided chemically 

 inert particles increases the rate of evolution of gases from liquids in 

 which they are being formed. The effect of these particles on the 

 following chemical changes is investigated : (i) the decomposition 

 of formic acid yielding carbonic oxide ; (ii) the decomposition of 

 ammonium nitrite in aqueous solution yielding nitrogen; (iii) the 

 reduction of nitric acid into nitric oxide by means of ferrous sulphate ; 

 (iv) the decomposition of ammonium nitrate in a state of fusion pro- 

 ducing nitrous oxide ; and (v) the decomposition of potassium chlorate 

 in a state of fusion producing oxygen. The finely divided substances 

 used are pumice, silica, graphite, precipitated barium sulphate and 

 glass-dust. 



Part II. — It is observed that, conditions of temperature remaining 

 the same, the rate of evolution of a gas from a liquid is at first slow, 

 then gradually increases until it reaches a maximum and for some 

 time constant rate. From this point the rate decreases proportionally 

 to the diminution of mass. This is observed in the cases of the decom- 

 position of formic acid, potassium ferrocyanide, and of oxalic acid by 

 concentrated sulphuric acid, and in that of ammonium nitrate. It 

 has previously been observed in the case of the decomposition of 

 ammonium nitrite in aqueous solution. The same phenomenon 

 repeats itself when the temperature is temporarily lowered and then 

 raised to its former point, and also to a more marked degree when, 

 temperature remaining the same," the superincumbent pressure is 

 suddenly increased. 



The reduction of pressure from one to a fraction of an atmosphere 



