Page:Experimental researches in chemistry and.djvu/394

1858.] 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 270° 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 substances to withstand a change of temperature, which, without the cohesion, ought to have caused a change of state. The efect 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 preparation before their adhesion to fluid is at a maximum: glass will permit water to boil in contact with it at 212°, or by preparation 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