Service chemistry : being a short manual of chemistry and metallurgy and their application in the naval and military services / by Vivian Byam Lewes and J.S.S. Brame.

  • Lewes, Vivian B. (Vivian Byam), 1852-1915.
Date:
1913
Catalogue details

Licence: In copyright

Credit: Service chemistry : being a short manual of chemistry and metallurgy and their application in the naval and military services / by Vivian Byam Lewes and J.S.S. Brame. Source: Wellcome Collection.

    110/622 (page 88)
    The mineral constituents of coal, other than the i:>yrites, ere the only ones that pla}^ no part in the phenomena attendmg the heating and spontaneous ignition of coal, and we must, therefore, consider the actions which take place when the carbon, hydro- carbon, and pyrites in freshly-won coal come in contact with air and moisture. Absorptive Power of Coal.—Certam kinds of coal exhibit the same power of absorbing gases which charcoal has, although to a less degree. The absorptive power of new coal due to this surface attraction varies, but the least absorbent will take up one and a quarter times its omi volume of oxygen, whilst some coals absorb more than three times their volume of the gas, which gives rise to an increase in temperature, and tends to accelerate the action which is going on, but is rarelj^ sufficient to bring about spontaneous ignition, only about one-third the amount of oxygen being absorbed by coal that is taken up by charcoal, and the action being much slower, tends to prevent the temperature reaching the high ignition point of the coal. All coal contains a certain proportion of hydrogen combined with carbon, and these, together with the nitrogen and oxygen, form the volatile matter in the coal. The amount of this volatile matter varies greatly, anthracite containing the smallest quantity, and cannel and shale the largest. A^Tren the coal absorbs oxygen the compressed gas becomes chemically very active, and soon commences to combine with the carbon and hydrogen of the resinous portions, converting them into carbon dioxide and water vapour. As the temperature rises this chemical activity in- creases, so that the heat generated by the absorption of the oxygen causes it to rapidly enter into chemical combination. This kind of chemical combination—oxidation—is always accompanied Ity heat, and this further rise of tenq^erature helps the rapidity of oxidation, so that the temperature lises steadily ; and this taking ]jlace in a large mass of coal, which finm physical causes is an admirable non-conductor, it will often cause such heating of tlu' mass that if sufficient air can pass into the liea]) in order to con- tinue the action, the igniting point of the coal will be reached. It is well knovn that bituminous coals exjiosed to the air for any length of time i-apidly lose their power of coking when carbon- ised, and also undergo considerable loss in calorific value, this action, which is called “ weathering.” being due to oxidation of the resinous constituents.