48 SCIENTIFIC AGRICULTURE. 



nitrogen, arc not, according to Dr. Kane and others, in a state 

 of chemical union, but only a mixture. 



The specific gravity of air is about 7 SO times less than that 

 of water; 100 cubic inches weigh about 31 grains. A column 

 of air 45 miles high just balances a column of water of the 

 same diameter, 33 feet high, or a column of mercury 29 

 inches high : hence water cannot be raised in a pump on the 

 principle of atmospheric pressure, more than about 33 feet, 

 hence also the mercury in the barometer tube is about 29 

 inches high. The air expands and becomes less dense by 

 heat ; hence warm air always rises, and cold air descends : the 

 composition of the air is everywhere nearly uniform, its com- 

 plete and beautiful adaptation to the wants of animal and 

 vegetable life will be more apparent the more we become 

 acquainted with its nature and laws : without it no animal or 

 plant could exist for a single day. Its relations to vegetation 

 more especially, will be described hereafter. 



CARBONIC OXIDE. 



Carbonic oxide is a colorless, inodorous gas, composed of 

 one equivalent of carbon, united to one of oxygen : it extin- 

 guishes a lighted taper, takes fire at the same time itself, and 

 burns with a pale blue flame, forming carbonic acid. It is 

 lighter than common air, nearly insoluble in water, and does 

 not support animal life. It is produced, together with car- 

 bonic acid, by the combustion of coal fires. " It is not known 

 to occur in nature, or to minister directly to the growth of 

 plants." 



OXALIC ACID. 



This is another compound of carbon and oxygen, in the 

 proportions of two of the former to three of the latter. It is 

 found in the interior of many plants, as the sorrel, rhubarb, 

 bistort, gentian, chick pea, and several lichens : it is not known 

 to contribute to their growth, but appears to be the result of a 



