1858.] On Regelation. ^ 379 



In the other direction, Donny's experiments have taught us 

 that the cohesion amongst the particles of water is so great 

 that it will support a column of the fluid four or more feet 

 high when there is no other power to sustain it ; or will cause 

 it to resist conversion into the state of vapour at temperatures 

 so much higher than its ordinary boiling- or condensing-point, 

 that explosion will occur when the continuity, and therefore 

 the cohesion, is destroyed. The water may be exalted to the 

 temperature of 70 Fahr. at the ordinary pressure of the 

 atmosphere, and remain as water ; but the introduction of the 

 smallest particle of air or steam will cause it at once to burst 

 into vapour, and at the same time its temperature falls. 



This ability which water has to retain by cohesion its liquid 

 state, refusing to solidify when below the freezing-point, or 

 to become vapour when above the boiling-point, it has in 

 common with many other substances. Acetic acid, sulphur, 

 phosphorus, many metals, many solutions, may be cooled 

 below the congealing temperature prior to the solidification of 

 the first portions ; many other substances, such as alcohol, 

 sulphuric acid, ether, camphine, &c., boil with bumping, or 

 boil with different degrees of facility in vessels of different 

 substances*. The conclusion, that these differences are due 

 to a certain range of cohesion in the case of each body, seems 

 tome both simple and natural ; this cohesion enabling the sub- 

 stances to withstand a change of temperature, which, without 

 the cohesion, ought to have caused a change of state. The 

 effect of extraneous matters as nuclei also appears to me to 

 be simple ; for though when introduced, as into cooled or heated 

 water, their particles may exert a cohesive force (so to say) 

 upon the particles of the fluid, the force so exerted in the first 

 instance is rarely equal to the force exerted between the water 

 particles themselves. Extraneous substances require prepa- 

 ration before their adhesion to fluid is at a maximum : glass 

 will permit water to boil in contact with it at 212, or by pre- 

 paration will remain in contact with it at 270 Fahr., as in 

 Donny's experiment. It will also remain in contact with water 

 at 22 Fahr. without causing its solidification, and yet an 

 ordinary piece of glass will set it off at once. 



Enough has been said, I think, to show that water particles 



* Marcet. 



