A 



238 PARING AND BUKNING. 



the surface, had a temperature of 39 degrees. This slight 

 elevation of temperature was enough to allow the gaseous 

 exhalation of organic matter, which was found to exceed 

 that of fresh fallen snow by 20 times. This quantity, in 

 snow 3 inches deep, would give per acre 40 lbs., and to this 

 are to be added 5 lbs. of salts. If this geirie is not a natural 

 addition in weight, it has undergone a transformation and 

 become soluble. Besides, every inch of fresh fallen snow 

 actually adds a little of this same matter ; it will not be 

 extravagant to estimate the total addition of geine at 50 lbs. 

 per acre for the winter. This, added to the warming effects 

 of snow, shows that it may have a genial and enriching 

 power on vegetation, independent of its ammonia. The old 

 notion of the existence of nitre in snow is not supported by 

 evidence ; but in whatever view we consider the salts of lime 

 in snow and rain water, it is difficult to believe that carbon- 

 ate of ammonia exists in atmospheric air. 



287. There are still other sources of manure, or the ele- 

 ments of fertility, which the farmer can command. Among 

 these are paring and burning and the ploughing in of green 

 and dry crops. 



It is not intended to go into the detail of these operations. 

 All experience proves their great fertilizing power. Their 

 whole action, mysterious as a part of it may appear, depends 

 for its success upon the formation of geine, salts, and silicates. 

 And first, — burning, in which is to be considered the effects 

 of simply burning the earthy parts of soils. In the descrip- 

 tion of silicates, Chap. II., the frequent occurrence of pyrites, 

 or sulphuret of iron, was described, and this is especially 

 the case in all clays. The effect of burning is, to disengage 

 sulphurous acid, and the red and seared appearance of the 

 foliage in the neighborhood of a brick kiln, which may be 

 often observed, is due to the disengagement of acid gases, 



i 



