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.

    109/710 (page 87)
    whilst if the ignition point be above the ordinary tempera- ture ignition has to be set up by raising the temperature to the necessary point. When combustion is in this way started, if the heat evolved by the action raises the temperature above the ignition point of the burning body, combustion continues until the combustible has burned away; but if the heat generated be insufficient to raise the body to its ignition point, the combustion ceases as soon as the external heating is removed. The combination of nitrogen and oxygen is a good example of this latter class of phenomena, as, although they will combine at the temperature of the electric discharge, the combination does not emit sufficient heat to continue the combustion, and it is upon this that the safety of the atmosphere depends. All ordinary cases of combustion belong to the first class, and the heat evolved when once the point of ignition is reached carries on the action. Spontaneous Ignition or Combustio7i.—During the decay or slow oxidation of combustible bodies heat is generated, and that it is only necessary for this heat to reach a certain point, i.e., the point of ignition, for the little noticeable slow combustion to become ordinary combustion with its mani- festation of flame or incandescence, and it is this action to which the term spontaneous combustion has been given. When the combustible substance has a great affinity for oxygen, and at the same time a low point of ignition, spontaneous combustion will take place with great ease. Indeed, in some cases, such as that of phosphorus, we are obliged to prevent the access of air to the body if we wish to prevent ignition taking place, and we also find that the finer the state of division of the substance the more readily will its spontaneous ignition take place, not because sub-dividing the body in any way lowers the point of ignition, but because the surface exposed