EVOLUTION OF GASES FROM HOMOGENEOUS LIQUIDS. 261 



PART I. 



EFFECT OF FINELY DIVIDED PAKTICLES ON THE RATE OF EVOLUTION OF GASES, 

 RESULTING FROM A CHEMICAL CHANGE OCCURRING IN A HOMOGENEOUS LlQUTD. 



The effect of finely divided particles or of roughened surfaces in promoting the 

 evolution of gases from their solutions in liquids, and that of vapours from liquids in a 

 state of ebullition is well known. The former phenomenon has been investigated by 

 OERSTED, SCHONBEIN, LIEBIO, GERNEZ, SCHRODER, and TOMLINSON, and the latter by 

 WATT, GAY LUSSAC, MARCEL, MAGNUS, DONNY, and GROVE. GERNEZ* attributes the 

 effect of these particles in increasing the evolution of carbonic acid from its super- 

 saturated solutions to air bubbles contained within them, an explanation shown to be 

 inadequate. ToMLiNSON.t by similar experiments, distinguishes between surfaces 

 which are and are not " chemically clean." From clean surfaces, such as that of a 

 freshly broken flint, or of a metal carefully washed with alcohol, no gas bubbles are 

 given off; but when these surfaces are rubbed with a cloth and reintroduced into the 

 solution of carbonic acid, they are immediately studded with bubbles of gas. He 

 writes, " Make the solids chemically clean, and the solution adheres to them without 

 any disengagement of gas ; make them unclean, and then the adhesive force of the 

 solid becomes more energetic for the gas than for the liquid, and there is a consequent 

 separation of gas from the liquid." The experiments of SCHRODER}; are of a similar 

 kind. These phenomena, though analogous to those to be described below, are in this 

 sense different, that in the one case we are dealing with a ready-made solution of a gas, 

 but in the other with a gas in the course of manufacture from the material contained 

 in a solution. 



In an experiment an aqueous solution of sodium formate, containing 1 gram of 

 the salt, was added to such a previously-made mixture of sulphuric acid and water 

 that the composition of the whole, before the reaction set in, was in the ratio 

 1H 2 () : 3H 3 SO 4 . An evolution of carbonic oxide resulting from the chemical change 



HCOOH = CO + OHj 



* ' Compt, Rend.,' vol. 63, 1866, p. 883. 



t ' Phil. Mag.' vol. 34, pp. 136 and 229 : vol. 38, p. 204 ; vol. 43, p. 205 ; and vol. 45, p. 276. 



J ' POOOENDOBFF, A imiili-ii,' vol. 137, p. 76 ; and Erganznngsband 5, p. 87. 



Mr. HARCOURT tells me that his attention was called to this subject nearly thirty years ago, when, in 

 attempting to concentrate hydrogen dioxide under the receiver of an air-pump, he found that the decom- 

 position of the liquid was hastened by removing the atmospheric pressure. Subsequently, ho tried to 

 measure tho rate of decomposition of hydrogen dioxide under constant conditions, and had, finally, to 

 abandon the attempt, in consequence of the impossibility of fixing one condition, namely, the state of tho 

 surface of the glass vessel which held the liquid. If the vessel was scrupulously cleaned, the decompo- 

 sition took place more quickly than if any trace of grease adhered to the glass, and more quickly with 

 some kinds of glass than with others. July 26th, 1888. 



