Notes on Organic Chemistry. 429 



ration, and certain kinds of decay, take place as results of 

 oxygen combining with the thing or things said to be burnt. 

 Oxygen is rather heavier than common air, its specific gravity 

 being 1*1056. In addition to its largely entering into the com- 

 position of water and air, it constitutes at least one- third of the 

 known constituents of the solid globe. 



Hydrogen is the lightest known substance; a given quantity 

 only weighs one-sixteenth as much as the same quantity of 

 oxygen. In contact with or mixed with oxygen it is capable 

 of burning, and the product is water, of which it constitutes 

 one-ninth by weight. 



Nitrogen is remarkable for its negative qualities when 

 isolated, and for the active properties of many of its compounds. 

 When mingled with oxygen to form air, it reduces the force 

 with which its more active companion operates upon organic 

 and inorganic substances. It will neither burn nor allow what 

 are called combustibles to burn in it. Like hydrogen, it is not 

 adapted to respiration. Although it does not burn in oxygen, as 

 hydrogen does, it combines with that gas under appropriate 

 conditions, and in various proportions. One of these com- 

 pounds, nitric acid, is a substance that acts with destructive 

 energy upon organic bodies. 



Carbon, in a pure crystalline state, presents itself as the 

 diamond, while various forms of charcoal, graphite, etc., exhibit 

 the same substance in an amorphous condition, and with more 

 or less impurity. In some states, carbon readily burns in an 

 atmosphere of oxygen, or common air, so soon as it is brought 

 to a red heat. In other conditions it is very difficult to burn at 

 all. The result of its direct combination with oxygen, through 

 combustion, is carbonic acid — the gas that effervesces in soda 

 water and ginger beer. 



Oxygen, hydrogen, nitrogen, and carbon all stand on the 

 list of the chemist's "elementary substances;" that is to say, 

 they have hitherto resisted all efforts to decompose them. 



They all exist in the mineral world, in plants and in animals. 

 In the first, they form compounds with each other, or with 

 other substances, the general characteristics of which is sim- 

 plicity ; in the second and third, they form other compounds, 

 the general character of which is complexity. 



Those who have not mastered the elements of chemistry 

 may understand this paper, if, in addition to the facts already 

 cited, they will for a moment consider the character of chemical 

 composition. If we make a mixture by rubbing up two bodies, 

 such as chalk and charcoal, our microscopes would show little 

 unchanged particles of each, lying side by side. If we mix 

 oxygen and nitrogen so that the compound contains 21 parts 

 of the former, and 79 parts of the latter, we shall have manu- 



