42 Keport of the Acting Director and Chemist of the 



in the manufacture of lead-pencils ; (3) ordinary wood-charcoal ; (4) 

 lamp black; (5) animal charcoal ; (6) mineral coal. Excepting dia- 

 mond these forms of carbon are more or less impure, containing 

 some other things mixed with the carbon. 



Hydrogen. — {a) OcGurrence. — The element hydrogen is nearly 

 always found combined with other elements. It combines with 

 oxygen to form water. Hydrogen also occnrs in most animal and 

 vegetable substances, such as various kinds of wood, fruits, etc., in 

 which it is combined with the elements, carbon and oxygen. Hydro- 

 gen is always present in all kinds of acids. 



(5) Desc^'ijHion. — Hydrogen, in the uncombined form, is a gas 

 that resembles air in that it has neither color, smell, nor taste. 



Oxygen. — {a) Occurrence. — Oxygen is the most abundant of all 

 the elements. The compounds which contain no oxygen are few in 

 number. Oxygen forms nearly one-half of the crust of the earth ; 

 eight-ninths of water ; about one-fifth of air ; and one-third of all 

 animal and vegetable matter. 



Oxygen occurs in the air uncombined with other elements. 

 Oxygen, combined with the elements carbon and hydrogen, or with 

 carbon, hydrogen and nitrogen, is found in substances which go to 

 make up animals and vegetables. 



(h) Descrvption. — As might be inferred from knowing that 

 oxygen in the uncombined state forms part of the air, oxygen is a 

 gas having no color, taste or smell. 



Oxygen is a very active substance from a chemical point of view. 

 It tends to unite with nearly all of the elements. In all forms of 

 burning, the oxygen of the air is simply imiting with otlier ele- 

 ments. Thus, in a coal fire the oxygen unites with the carbon of 

 the coal. The heat is produced by the union of the two elements. 



Nitrogen. — («) Occurrence. — Nitrogen occurs in nature in the 

 following fonns : 



(1) As a constituent of air. 



(2) In the foi-m of ammonia. 



(3) In the form of niti'ic acid and nitrates. 



(4) In various other forms in plants and animals. 



(1) Nitrogen in Air. — Nitrogen, uncombined with other elements, 

 forms about four-fifths of the air. Since the nitrogen in the air is not 

 combined, we can perceive its projDerties for ourselves, and our obser 

 vation shows us that it is a gas, which has neither color, taste nor smell. 



