Action of the Atmosphere upon newly-deepened Soil. 429 



that there may ])e more than one compound included under the 

 name. It contains at any rate oxygen in large quantity, if in- 

 deed it is not, as Faraday has hinted, merely that element ren- 

 dered more energetic in its action. Schonbein himself regards it 

 as a combination of oxygen and hydrogen. Its action appears to 

 be that of rapid oxidation, changing protosalts into persalts, 

 sulphurets into sulphates, nitrous acid into nitric acid, and so on : 

 it acts most powerfully upon metallic bodies, and destroys organic 

 substances even when diluted with much air or oxygen, and 

 bleaches vegetable colours like chlorine. Uniting readily with 

 fcEtid gases, it has a most beneficial effect in purifying the air, 

 and it is accordingly supposed that this property of thunder- 

 storms can be accounted for by its production during their con- 

 tinuance. In some large towns, such as London and Manchester, 

 it has not been met with ; but as its presence in the atmosphere 

 would appear to be pretty general, its action on the soil should 

 not be overlooked. 



Nitroc/en. — The uses of the nitrogen of the atmosphere are not 

 well understood ; it has been thought to act chiefly as a diluent 

 of the oxygen. It is a transparent colourless gas, rather lighter 

 than common air, and is distinguished more by its negative pro- 

 perties than by any striking quality of its own : its compounds 

 are generally easily decomposed. It is, however, an important 

 and necessary ingredient in organic bodies, and is found in plants 

 to the extent of from 1 to 4 per cent., and, in union with 

 hydrogen, it forms the important compound ammonia, and it is 

 chiefly through this medium that it has been thought to enter 

 into the structure of plants. It occurs but very sparingly in 

 the minerals of the soil, and hence the necessity of supplying it 

 in manure : 100 cubic inches of boiled water absorb, according 

 to Dalton and Henry, 1'56 cubic inches of nitrogen. 



Carbonic Acid is not, like the two former, an elementary or 

 simple sulistance, but is a combination of carbon and oxygen. 

 Forming but a small proportion of the atmosphere compared with 

 the nitrogen and oxygen, its relations to plants are yet most im- 

 portant, and the action of the air upon the soil is largely depen- 

 dent upon it. Nearly 50 per cent, of tlic dry substance of plants 

 consists of carbon ; and as this is supposed to be derived from the 

 carbonic acid wiiich thov absorlj, we may look ujion the latter as 

 the mf)st imj)ortant food of vegetables. The carl)(m of animals is 

 also derived from the same source. This gas is absorbed by water 

 to an extent ])roportional)le to the pressure, the water taking up 

 about its own volume ; if the pressure, therefore, is great, a very 

 large fjuantity of xXw. gas will l)e held in solution, as is seen in 

 champagne and other cfFervescing liquors. Tlie addition of a little 

 carbonate of soda will make the water absorb a still greater amount 



VOL. XVII. 2 G 



