Service chemistry : being a short manual of chemistry and its applications in the naval and military services / by Vivian B. Lewes and J.S.S. Brame.

  • Lewes, Vivian B. (Vivian Byam), 1852-1915.
Date:
1906
Catalogue details

Licence: In copyright

Credit: Service chemistry : being a short manual of chemistry and its applications in the naval and military services / by Vivian B. Lewes and J.S.S. Brame. Source: Wellcome Collection.

    130/710 (page 108)
    3. The volume of the gas absorbed varies directly as the pressure; that is to say, at all pressures the water absorbs the same volume of gas, since the volume of the gas itself varies inversely as the pressure. This is taken advantage of in the manufacture of aerated waters. Carbon dioxide gas is absorbed by water under pressure, the amount dissolved depending upon the pressure; this pressure is then kept constant by the bottle being corked and wired, but when the cork is removed the liquid is now under ordinary atmospheric pressure, and can only hold in solution the volume of gas corresponding to that particular pressure, the excess escaping and causing the effervescence. The solution of solids, like the solution of gases, depends largely upon the nature of the solid ; one litre of water will dissolve O’lq grams of strontium sulphate and nearly i,oco grams of magnesium sulphate. The rate of solution is increased by the fineness of division and by agitation of the liquid, as, if the liquid be quite still, the layer of water next the solid becomes saturated, and being therefore denser protects the remainder, solution only proceeding by liquid diffusion, a process infinitely slower than gaseous diffusion. The solubility of a salt, as a rule, increases with the temperature of the water, but strontium sulphate and lime are exceptions, being more soluble in cold than hot water. Water of Crystallisation.—When a point is reached at which no more of the solid can be dissolved, the liquid is said to be saturated, and if allowed to stand so that the water can cool or evaporate, the solid will again separate out—often in the crystalline form, and this form is in many cases due to water held in a feeble state of combination, and called water of crystallisation. For instance, sodium carbonate crystallises with ten molecules of water of crystallisation, and these crystals when exposed to air