208 On the Formation and Decomposition of Carbonic Acid. 



carbonic acid, while the straw and other residue slowly assume 

 the same form. But the food sold is derived from fertility 

 stored up in the soil, accumulated by vegetation in ages long- 

 past, and thus goes also to swell the amount of carbonic acid 

 contributed by the soil to the atmosphere. 



This is made perfectly clear by long-continued experiments 

 at Rothamsted, which show that crops raised on unmanured 

 land, as also upon land receiving the mineral food of plants 

 but no nitrogen, derive their nitrogen from the store in the 

 soil ; and as this nitrogen exists in combination with carbon, 

 the latter is given off in the form of carbonic acid. Further, 

 as agriculture is generally attended with more or less exhaus- 

 tion of the soil, there is, in consequence, a slight increase in 

 the carbonic acid added to the atmosphere by cultivation. 



This is more clearly seen when we consider that most of the 

 land which is now in cultivation was previously woodland or 

 pasture. At Rothamsted we have found by analysis that the 

 pasture contains more than twice as much organic carbon and 

 nitrogen as the arable land — a result which may be attributed 

 to the fact that on the latter these substances have been gra- 

 dually destroyed or carried off by cultivation. On the other 

 hand, in cases where arable land has been converted into per- 

 manent pasture, carbon again becomes fixed in the soil, both 

 as roots in living vegetation and as organic carbon. 



It is true that on land which receives a large dressing of 

 dung annually we have found a very considerable increase of 

 the carbon in the soil ; in gardens also, in land laid down to 

 pasture, and woodlands (especially newly planted woods) car- 

 bon would be abstracted from the air ; but, generally speaking, 

 I think that more carbon is given off from the products of the 

 soil of Great Britain than is fixed by the living vegetation. 

 If, in fact, we were entirely dependent on the atmosphere 

 resting upon our country for existence we should very soon 

 perish. 



A process very similar to what I have described, though 

 not to the same extent, is going on throughout the world : 

 population and animals increase, fuel is burnt, forests are 

 destroyed, and the stores of carbon and nitrogen accumulated 

 in the soil by natural vegetation are slowly dissipated. We 

 must look, therefore, to some other source, rather than to the 

 land, for the restoration of the balance. 



It is quite possible that this source is to be found in the 

 ocean. According to analyses made by Dr. Frankland, the 

 sea, even at a great depth, is very rich in organic carbon and 

 nitrogen ; it also contains large quantities of nitric acid ; and 

 these quantities are being increased from day to day by fresh 



