28 Retarded Ebullition — Boiler Explosions. 



RETARDED EBULLITION— BOILER EXPLOSIONS. 



Professor Dufour, of Lausanne, has a long and interesting 

 paper on the " Retardation of the Ebullition of Water, and on 

 a Probable Cause of Explosion in Steam-Boilers," in the 

 Archives des Sciences, No. 83. We shall select the prominent 

 passages, which will show the character of the facts which 

 recent researches have made known in reference to these 

 questions. 



M. Dufour commences by observing that - the law usually 

 admitted as denning the relation between the boiling point of 

 any liquid, and the pressure upon it, is subject to numerous 

 exceptions. Gay-Lussac observed that the boiling point 

 of water and other liquids was retarded by glass vessels. 

 More recently MM. Marcet, Donny, Magnus, and others, have 

 written on the subject, and Mr. Grove has described experi- 

 ments in boiling water more or less deprived of air, and he 

 has remarked that no one has yet seen the ebullition of per- 

 fectly pure water. Three years ago M. Dufour published an 

 account of observations on water and other liquids heated in 

 the midst of a fluid of the same density, and consequently 

 withdrawn from contact with the solid walls of the containing 

 vessels. Under such conditions water could be heated to 

 170° C, chloroform to 100°, etc. From such facts it appears that 

 a temperature which gives to the vapour of any liquid a ten- 

 sion equal to the external pressure, is the minimum tempera- 

 ture at which it can boil; but the temperature at which it 

 does boil will depend upon the conditions to which it is ex- 

 posed, and especially those of contact with solids or gases. 



After describing the apparatus which he employed, M. 

 Dufour gives the following results : — " When after a first 

 heating, not carried to the boiling point, the water is allowed 

 to cool and arrive at a given temperature (t) : if the pressure 

 is diminished until it becomes equal to the elastic force of 

 vapour at that temperature, boiling occurs exactly at the 

 point required by Dalton's law, or a few tenths of a degree 

 below it." 



" When the liquid has boiled for some minutes before 

 being allowed to cool, and suffer the diminished pressure, 

 sometimes it will commence ebullition the moment the 

 elastic force of its vapour equals the pressure, while at other 

 times ebullition will be retarded more or less considerably." 



"When the liquid has been boiled three, four, five, or 

 more times before being allowed to cool, and suffer diminished 

 pressure, the retardations of boiling become much more fre- 

 quent and form the rule not the exception, . . . some- 



