A manual of physics, theoretical and practical : for medical students / by Hugh C. H. Candy.

  • Candy, Hugh Charles Herbert, 1859-1935
Date:
1918
Catalogue details

Licence: In copyright

Credit: A manual of physics, theoretical and practical : for medical students / by Hugh C. H. Candy. Source: Wellcome Collection.

    85/470 (page 71)
    heavy brine does not, however, remain at the bottom without mixing with the lighter water above. The molecules of the salt seem in solution to range farther and farther from each other, just as do the molecules of a gas, when the pressure is diminished, and to penetrate or diffuse into the water. This process of diffusion proceeds until, after the lapse of some time, the salt is evenly distributed throughout the water. The rate at which this diffusion of a substance takes place depends (I) on the nature of the substance; (2) on the strength of the solution, a 3 per cent, solution diffusing three times as quickly as a 1 per cent, solution ; (3) on the temperature, the rate increasing as the temperature rises. Relative times of diffusion of equal amounts of—■ Albumin . . . . 49'00 units. Magnesium sulphate , , T'OO ,, Sodium chloride , . . 2’33 ,, Hydrochloric acid . . O'l unit. So that hydrochloric acid diffuses 490 times as quickly as albumin. Graham observed that substances which diffused quickly were crystalline, and that those which dif¬ fused slowly were not, so he divided substances into crystalloids, such as salt, and colloids (from Ko\\ufdr]Q = viscous or glue-like), such as gelatin, albumin, etc. We now recognize that many substances which would not have been classed by Graham as colloids can be made to assume a colloidal state, e.g. ferric hydroxide, arsenious sulphide, gold, platinum; the word now denotes a condition of matter rather than a distinct class of bodies. Many phenomena, indeed, suggest that we have in this colloidal condition a sort of half-way house between liquid and solid—a state of molecular aggregation intermediate between that