A treatise on chemistry. Vol. 1, The non-metallic elements / by Sir H.E. Roscoe & C. Schorlemmer ...

  • Roscoe, Henry E. (Henry Enfield), 1833-1915.
Date:
1881
Catalogue details

Licence: Public Domain Mark

Credit: A treatise on chemistry. Vol. 1, The non-metallic elements / by Sir H.E. Roscoe & C. Schorlemmer ... Source: Wellcome Collection.

Provider: This material has been provided by University of Bristol Library. The original may be consulted at University of Bristol Library.

    61/792 (page 45)
    Priestley when he discovered oxygen, may serve as an illustra- tion of a chemical decomposition. 2'16 grams ^ of red oxide of mercury are heated in a small retort provided with a receiver, and a gas delivery tube passing to the top of a graduated cylinder filled with water to the beginning of the graduations, and standing in the pneumatic trough over water (Fig. 4). On heating the red oxide by means of the Bunsen's gas flame, it first becomes dark- coloured and then soon begins to decompose into metallic mercury, which collects in small bright drops in the neck of the retort gradually running down into the receiver, and into ox3^gen gas, wliich passes through the delivery tube and collects in the graduated cylinder. After the heat has been continued for some time, the whole of the red powder will have disappeared, having been changed by heat into metallic mercury and oxygen. Fig 4. On allowing the retort to cool, a volume of 112 cubic centi- metres of gas has been collected, and this, on application of the red-hot chip test, is shown to be oxygen. If this experiment is properly conducted, the volume of oxygen obtained is always found to be the same from the same weight of oxide (provided the temperature and pressure at which the gas is measured are the same in the different experiments), viz., 112 cubic centi- metres from 2'16 grams of oxide. Another interesting case of chemical cliange is the decompo- sition of water by galvanic electricity as discovered by Nicholson ' For a talile of pqiiivalciiit values of tlic oommoii F.iif^lisli weights and measures, ■with tiiosc of the nictrical system, .see Apiicii Ji.x to tliis vohiuie.