210 ATMOSPHERE IN RELATION TO HUMAN LIFE AND HEALTH. 



Ozone is formed by the passage of the electric spark, and especially 

 of the brisk discharge through oxygen, and is therefore found in 

 unusual quantity after thunderstorms. It may also be formed by the 

 slow oxidation of phosphorus, and of essential oils in the presence of 

 moisture; also by the decomposition of water by a galvanic current. 

 When formed by electric discharge in air, it is quickly turned back 

 again into oxygen, either by further discharges or by the action of high 

 temperature, about 230° C; at the temperature of boiling water it is 

 slowly decomposed in moist air. Its pungency of odor is said to make 

 it easily perceptible when only present to the extent of 1 volume in 

 2,500,000 volumes of air, and the smell may sometimes be noticed on 

 the seabeach. It has been liquefied at 100° C. under 127 atmospheres 

 pressure. In this form it shows a dark indigo-blue color; gaseous 

 ozone looked at in a tube 1 meter long also shows a blue color. Thus 

 there can be little doubt that, in conjunction with oxygen and fine dust, 

 it contributes to the azure hue of the sky. 



NITROGEN. 



Mtrogen, the gas which constitutes four-fifths of the volume of the 

 atmosphere, takes no direct part in the sustenance of human life, but 

 has two great functions to perform: first, the dilution of oxygen to the 

 proper and tolerable strength for respiration, and secondly, the supply 

 of food material to plants. 



Although life is possible for many hours in pure oxygen, it is hardly 

 conceivable that the human constitution could be so modified as to 

 endure for long an atmosphere of so actively combustible a character. 

 At any rate, nitrogen is indispensable in present conditions to the 

 human race. Plants, with few exceptions, do not absorb nitrogen from 

 the air, and, indeed, in the case of most of these exceptions the supply 

 of nitrogen is in a transitional compound form. Mtrogen is brought 

 to the plants in general by processes of decay, and by the action of 

 microbes in the soil, which rearrange organic elements, forming nitrates 

 and nitrites. These nitrogen compounds are largely applied to the 

 roots of plants as manure. Only one or two classes of plants can take 

 up nitrogen from the air. Certain low algse, freely exposed to light and 

 air, seem to absorb nitrogen directly. Leguminous plants, such as 

 peas, vetches, lupins, beans, clover, etc., absorb nitrogen from the air 

 in a very curious way. Nodules or swellings are found on the roots; 

 these contain minute fungi or microbes ; the bacteria absorb nitrogen 

 from the air, and, probably at the expense of the energy of the carbo- 

 hydrates, etc., which they oxidize, supply this nitrogen in the form of 

 compounds to the plant. These recently discovered facts open out the 

 prospect of obtaining scientifically from the air, in some cases at least, 

 the nitrogen which is now applied in combination with oxygen, soda, 

 etc., as manure. If by the aid of special bacteria parasitic upon the 

 plant we can systematically obtain the chief element of manurial 



