Chemistry / by George Wilson.

  • George Wilson
Date:
1857
Catalogue details

Licence: Public Domain Mark

Credit: Chemistry / by George Wilson. Source: Wellcome Collection.

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    monia to form sal-ammoniac (NHSHC1), which is not volatile at 212° F. The acidulated liquid is then evaporated to dry- ness, and leaves a slight residue of ammoniacal salt, which, when mixed with quicklime, gives off its ammonia. This is easily recognised by its characteristic odour of hartshorn. 404. The uses of the several gases and vapours mentioned, are now pretty well ascertained. The importance of water-va- pour to animal a.nd vegetable life does not call for lengthened illustration. The oxygen supports the respiration of animals, entering their bodies by their lungs or other breathing organs, and effecting changes on the fluids and tissues, essential to the maintenance of life. Oxygen also enters plants, dissolved in the water which they absorb by their roots. 405. The nitrogen of the atmosphere serves to dilute the oxygen to the point, or strength most suitable for the wants of living beings. Animals made to breathe pure or undiluted oxygen are thrown into a state of fever, which quickly proves fatal. Nitrogen, however, also serves an important purpose in the economy of nature, by increasing the volume of the atmosphere without conferring upon it active chemical pro- perties. Provision is thus made for the occurrence of winds, the tempering of climate, the diffusion of heat, the scattering of the sun’s light, and the realisation of other useful ends essential to the welfare of man and the other living inhabi- tants of the globe. 406. The carbonic acid supplies plants with their most abundant element, which they obtain from it by decomposing it into its constituents, carbon and oxygen; the former they retain, the latter they restore to the atmosphere. This de- composition is effected chiefly by the leaves, but also by the other green parts of plants. It occurs only during the day; and to the greatest extent w-hen the sun is shining most brightly. During- darkness, plants totally lose the power of decomposing carbonic acid. This remarkable action of living- vegetables will be referred to again under the head of car- bonic acid. 407. The ammonia w-hich is constantly reaching the air, as a product of the decomposition of animal and vegetable matters, is brought down to the earth, as we have seen, by each shower that falls; and entering the roots of plants along w-ith the rain-water, supplies them with nitrogen, an ele- ment essential to their growth. This will be referred to again under the head of ammonia. 408. The physical properties of the atmosphere are of as much interest as the chemical, but cannot be discussed at length here. The height of the atmosphere is about forty-
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