1869.] in liberating Vapour from Boiling Liquids. 



241 



In 181 2, and again in 181 7, Gay-Lussac* noticed A chard's experiments on 

 the effect of the vessel on the boiling-point, and of metal turnings, charcoal 

 powder, and pounded glass in lowering it. He supposed the boiling-point 

 to vary in different vessels according to the nature of their surfaces, and 

 that the variation depends both on the conducting-power of the material 

 for heat and on the polish of the surfaces. When water is boiling in a 

 glass vessel, the temperature is higher than in a metal one ; but if a few 

 pinches of iron-filings be put in, the boiling goes on as in a metal vessel". 

 Without this aid the water boils in bursts, the steam having to overcome 

 the cohesion or viscosity of the liquid, and its resistance to change of state. 

 The adhesion of the liquid to the vessel must also be a force analogous to its 

 viscosity. The use of platinum is recommended for preventing soubresauts. 



In 1825 Bostcckf noticed that ether in a matras over a spirit-lamp 

 boiled at 112° F. ; but in a test-tube put into hot water it did not begin to 

 boil under 150°, and on one occasion 1/5°. Bits of cedar-wood put into 

 the ether made it boil at 110°; the wood was covered with bubbles until 

 (according to Bostock) having discharged ail its air, it became inactive and 

 sank. Bits of quill, feather, wire, pounded glass, &c. also lowered the 

 boiling-point considerably. A thermometer plunged into the ether pro- 

 duced bubbles many degrees below the point at which ebullition took place 

 when the thermometer was not inserted : this effect soon ceased ; but by 

 alternately plunging the thermometer into the ether and removing it, the 

 bubbles were produced at each immersion. 



LegrandJ in 1S35 also referred bursting ebullition and soubresauts to 

 the absence of air in the liquid. Many salts prevent soubresauts ; others, 

 such as the neutral tartrate of potash, favour them. 



In 1842 Marcet§- considered that iron, zinc, and other substances tend 

 to depress the boiling-point, because they have a less molecular adhesion 

 for water than glass has. If the vessel be coated with a thin layer of sul- 

 phur, gum-lac, or any similar substance that has no sensible adhesion for 

 water, the temperatures of the water and of the steam are alike. The 

 boiling-point varies in flasks of different kinds of glass, and in the same 

 flask at different times. In a flask used for holding sulphuric acid the 

 boiling-point of pure water was 106° C. These variations are referred to 

 molecular changes on the surface of the glass. 



In 1843 Donny|| referred to the powerful influence of air or gases dis- 

 solved in the liquid on the phenomena of ebullition ; but as his theory is 

 the same as that advanced by De Luc many years before, it is not necessary 

 to notice it further. 



In 1861 Dufour^[ described an experiment in which globules of water 



* Ann ales de Chiruie, vol. Ixxxii. p. 171 ; Annales de Chimie et de Physique, vol.vii. 

 p. 307. t Annals of Philosophy, ~N. S. vol. ix. p. HQ. 



| Annales de Chimie et de Physique, vol. lix. 



§ Annales de Chimie et de Physique, 3 e Serie, vol. v. p. 449. 



11 Memoires couronnes par l'Academie Eoyale de Bruxelles, vol. xvii. pub. 1845. 



^[ Archives de la Bibliotheque TJniverselle de Greneve. 



