Air, Atmospheric

(or simply, The Air). The air chiefly consists of a mechanical mixture of four volumes of nitrogen and one volume of oxygen, or more accurately— | By volume. | By weight. | | Nitrogen | 79·1 | 76·8 | | Oxygen | 20·9 | 23·2 | | ——— | ——— | | 100 | 100 [12] | [12] At a meeting of the Paris Academy of Sciences, held on the 31st of December, 1877, it was announced that M. Cailletet had succeeded in liquefying atmospheric air. We may premise our description of the functions of the constituents of the atmosphere by the following quotation from Mr Blyth’s ‘Dictionary of Hygiène and Public Health’:—“One of the most important properties of air is its power of penetration and its universality. Air is, indeed, present everywhere; there is scarcely a solid, however compact it may appear to be, which does not contain pores, and these pores filled with air. The soil contains no small quantity; indeed, if it were not so the numberle insects, worms, ., which burrow in its interstices would cease to exist. The most compact mortar and walls are penetrated with it, and water of natural origin contains a large quantity of air in solution. The atmosphere is supposed to extend to a very great height, from 200 to 300 miles; it used to be considered only five (forty-five) miles high, but observations on shooting stars, ., show that this opinion is erroneous. Owing to the force of gravity, the air is much denser near the earth, and gets more attenuated layer by layer as you ascend. If, then, the atmosphere were po e ed of colour, it would be very dark just round the globe, and the tint would gradually fade into space. The air is by no means wholly gaseous; it contains, indeed, an immense amount of life, and small particles derived from the whole creation. In the air may be found animalcules, spores, seeds, pollen cells of all kind, vibriones, elements of contagion, eggs of insects, ., and a few fungi, besides formle dust, sandy, and other particles of local origin; for example, no one can ride in a railway carriage without being accompanied with dust, a great portion of which is attracted by a magnet, and is, indeed, minute particles of iron derived from the rails. The purest air has some dust in it. There probably never fell a beam of light from the sun since the world was made which did not show, were there eyes to see it, myriads of motes; these, however, generally speaking, are quite innocuous to man—some, indeed, may po ibly be beneficial. Another most important property of air is its mobility; on the calmest day and in the quietest room there are constant currents of air which rapidly dilute any noxious odours of gases.” The chief functions of the oxygen are to maintain respiration and support combustion, while the office of the nitrogen is to dilute the oxygen and control its energy. Besides nitrogen and oxygen, aqueous vapour, carbonic anhydride, ammonia, and nitric acid are met with in the atmosphere, the last especially during and shortly after thunder storms. Although, doubtle owing to local conditions, trifling variations may occur in the proportion of oxygen present in the atmosphere, this variation is so trifling that the difference of the amount in air from places separated by very long distances will be found in the second decimal place only; thus, whilst a portion of air taken during a balloon ascent by Mr Green gave on analysis 20·88 per cent. by vol., Dr Frank land found in air collected by himself on the summit of Mont Blanc 20·96 per cent. by vol. A still nearer approximation in uniformity in the amount of oxygen present in atmospheric air is exhibited in the following table, which gives the results of 95 analyses by Regnault on air obtained from nine different localities:— | 100 | from Paris gave in 100 parts, by vol. of oxygen | 20·913 to | 20·999 | | 9 | from Lyons and around gave in 100 parts, by vol. of oxygen | 20·918 to | 20·966 | | 30 | from Berlin gave in 100 parts, by vol. of oxygen | 20·908 to | 20·998 | | 10 | from Madrid gave in 100 parts, by vol. of oxygen | 20·916 to | 20·982 | | 23 | from Geneva and Switzerland gave in 100 parts, by vol. of oxygen | 20·909 to | 20·993 | | 15 | from Toulon and Mediterranean gave in 100 parts, by vol. of oxygen | 20·912 to | 20·982 | | 5 | from Atlantic Ocean gave in 100 parts, by vol. of oxygen | 20·918 to | 20·965 | | 1 | from Ecuador gave in 100 parts, by vol. of oxygen | 20·960 | | 2 | from Pichincha gave in 100 parts, by vol. of oxygen | 20·949 to | 20·981 | | ——— | ——— | | Mean of all foregoing | 20·949 | 20·988 | | Mean of the Paris specimens | 20·96 | Vapour of water is e ential to the respiration of animals and plants, in order that the organs concerned in this operation may be kept in a soft and moist condition. Carbonic anhydride is evolved during combustion, putrefaction, and fermentation; it is also a product of the respiration of animals, and highly poisonous to them, even when diluted with large proportions of air. This gas is, however, greedily absorbed by plants, which decompose it; they a imilate the carbon and return the oxygen to the atmosphere, ready to be again consumed in supporting the life of the animal world. Dr Angus Smith has defined a very pure air to be one that contains with 20·99 per cent. of oxygen 0·30 of carbonic acid (anhydride). This latter varies in amount in the atmosphere of cities, as will be seen upon inspection of the subjoined table, extracted from Dr Smith’s work ‘Air and Rain’: — | Per cent. | | Air of Madrid, outside the walls, mean of 12 analyses, by Luna | ·045 | | Mean of 12 analyses, within the walls of Madrid, by Luna | ·051 | | Mean of 14 analyses, by Angus Smith, in Manchester suburbs | ·369 | | In Manchester streets | ·403 | | Usual weather | ·0403 | | During fogs | ·0679 | De Sau ure’s analyses show that there is more carbonic acid on the mountains than in the plains, as might be inferred from the comparative absence of vegetation in elevated positions. Dr Pietra Santa states that the air of hills or mountains, at the height of 2300 feet, is lighter than common air, contains a smaller proportion of oxygen, and is impregnated with a largely increased amount of aqueous vapour. It also contains a large quantity of ozone. He considers such a climate peculiarly soothing to persons suffering from chest diseases. Dr Angus Smith’s analysis of the air from the mountainous districts of Scotland confirms the above statement of Dr Pietra Santa’s. The heaths and mountains of that country are remarkably healthy localities, and the air from them gave on analysis 20·94 per cent. by vol. of oxygen, and only ·033 of carbonic acid. Ammonia is derived from the putrefaction of animal and vegetable substances. It is from atmospheric ammoniacal compounds that plants obtain much of the nitrogen which is e ential to the formation of many parts of their structure. Nitric acid, like ammonia, is absorbed, and its nitrogen a imilated, by plants. In addition to the gases and vapours already enumerated, as well as others which exist in minute quantity, or which are of only occasional occurrence, Pasteur and other investigators have discovered in the air living germs which are capable of exciting putrefaction and fermentation, and which are competent, in some instances, to engender disease when they are injected into the blood of animals. In fact, the spread of infectious diseases, e.g. , smallpox, typhus fever, cattle plague, ., is attributed to the presence in the atmosphere of the germs of such maladies. These germs are believed to be living beings, which develope and multiply at the expense of the ti ues of the larger animals into whose systems they have found entrance.