LECTURES AND ESSAYS READ AT INSTITUTES. 93 



very hot flame, and when it burns it combines with the oxygen of the air and 

 forms water, and hence called hydrogen. The oxygen does not burn, but 

 very intensely supports combustion, for a splinter with a live spark will burst 

 into flame when plunged into oxygen. The other gas neither burns nor sup- 

 ports combustion, and appears to be the laziest fellow in nature. This is 

 nitrogen and constitutes four-fifths of the volume of the air, the other fifth 

 being oxygen. Nitrogen is very abundant in the air, but in this form is 

 entirely useless for the plant, because plants cannot assimilate free nitrogen. 



II. Four are nonmetallic solids. Carbon is familiar to you all in char- 

 coal, and when you remember that all vegetable substances char or carbonize 

 when heated away from air, you recognize the fact that carbon exists in them 

 all. Silicon is a material resembling carbon in properties, but forms the basis 

 of sand. Sulphur is familiar to you all as brimstone. Phosphorus is a waxy 

 solid, and is the easily ignited substance in most friction matches. It burns 

 very easily, and when plunged into oxygen burns with great splendor. 



III. Five are metals; iron, with which are all familiar; potassium, the 

 silvery metal which is the basis of potash, and has such affinity for oxygen 

 that it takes fire when thrown into water. Sodium is a white metal resem- 

 bling potassium, and is the basis of soda, common salt, etc. Calcium is a 

 light metal, in color resembling gold. It is the basis of lime, the lime being 

 the oxide, or rust, of calcium. Magnesium is a silvery white metal, which 

 you see in the form of wire before you. It is the basis of magnesia. The 

 metal burns with great splendor, and forms magnesia, the oxide of magnesium. 



You will understand that none of these substances exist iu the separate or 

 elementary form in the plants, but in various forms of combination these 

 thirteen substances make up the whole of vegetable and animal substances — 

 this baker's dozen make up the cTiemicals of life. 



Small as is the number of these chemicals of agriculture, some are furnished 

 by the free hand of nature in such quantity that the farmer need take no 

 thought about their artificial supply. In the form of carbonic acid, carlon is 

 contained in the air in sufficient quantity to supply any crop, since there are 

 twenty-eight tons of carbonic acid in the air resting on every acre of the 

 earth's surface. The carbon is literally "as free as air." 



The oxygeyi and hydrogen are furnished in exhaustless quantity, and in just 

 the right proportions in water. One necessary physical condition of plant-life 

 is a supply of water, and in its presence the chemical conditions of growth, so 

 far as oxygen and hydrogen are concerned, are fully met. If the "early and 

 the latter rains" are denied, and the heavens withhold the benediction of the 

 sky, then "Bashan languisheth, and Carmel, and the flower of Lebanon." 



Sodium and Chlorine form common salt. The quantity required for most 

 crops is small, and a sufficient supply is usually found in the soil-water of 

 our State. The special uses of salt I will bring to your attention hereafter. 



Silicon is the basis of sand, and is a constituent of every rock except lime- 

 stone. Even the purest clay is a silicate of alumina. The soil supply of 

 silicon for all plants is inexhaustible, and all plants have the power of supply- 

 ing themselves with the necessary amount of silicon from the soil. 



Oxide of Iron is the chief coloring substance in our soils, and but for this 

 oxide and the organic matter of the soil, nearly all our soils would be white 

 as snow. The quantity of iron required in plant growth is exceedingly small, 

 and the soil supply is greatly in excess of the wants of agricultural plants. 



Calcium and Magnesium are the metallic bases of lime and magnesia. In 

 the form of carbonates they are found in most soils in sufficient quantity to 



