NITROGEN. 547 



14 inches), the hectare contains 3500 cubic metres of soU, the carbonic 

 acid in. the soil in proportion to that in the air, volume for volume, is 

 as 36:7. 



2. In the same quantity of land recently manured, the carbonic acid, 

 under certain circumstances, may be represented by that contained in 

 200,000 cubic metres of normal air, or in the proportion of 400 : 7. 



3. In the loamy subsoil of a forest, taking the average depth, as in 

 the former instances, the amount is that contained in 5000 cubic metres, 

 or as 10 : 7. There are of course more or less especi^il cases, for every 

 shade of difference is capable of occurring under peculiar data. In the 

 sandy subsoil of a forest, for instance, the proportion, as compared with 

 the loam in No. 3, was only as 1 : 2.76. 



Nitrogen, or azote, abounds in all the young parts, especially 

 while in rapid growth; as organs become old it disappears. 

 It is evidently connected with high vitality, whatever its exact 

 action may be ; and is as indispensable to the growth of a plant 

 as carbonic acid itself. The atmosphere consists of 79 per 

 cent, of nitrogen and 21 per cent, of carbonic acid. But 

 whether or not plants obtain their nitrogen in its pure state 

 from the atmosphere is uncertain. There is no doubt, how- 

 ever, that in the form of ammonia (an acrid gaseous compound 

 of nitrogen with hydrogen) it is eagerly consumed, provided it 

 is first reduced to the state of a soluble salt so as to lose its 

 causticity. The carbonate, sulphate, muriate and nitrate of 

 ammonia are all common forms of the substance, and being 

 soluble in water are readily absorbed by all parts of the live 

 surface of a plant. Lime has the power of decomposing these 

 salts and setting free their ammonia, for which reason lime 

 should never be used in conjunction with them. Nitric acid (a 

 compound of nitrogen with oxygen) is also another source of this 

 element, whence arises the great manuring value of nitrates ; 

 it exists abundantly in the atmosphere, as is shown by the 

 experiments of M. Barral, quoted at p. 29. 



Like carbonic acid, ammonia is condensed and detained in porous 

 bodies. Mr. Way was the first who drew attention to the remarkable 

 power which soils generally have of absorbing ammonia and its salts. 

 It had always been believed that all porous soils possessed the power of 

 condensing ammonia, and it had likewise been long known that, in 

 addition to this, which might be called a merely mechanical effect, certain 

 soils possess the power of absorbing or fixing ammonia, in consequence 



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