xii GENERAL INTRODUCTION 



burns so readily that it ignites by friction and is used in 

 matches. Rub the tip of a match with the finger. What 

 is the odor of phosphorus ? Phosphorus exists in nature 

 only in combination with other elements. Lead, tin, silver, 

 gold, copper, zinc, nickel, platinum, are elements. 



There are less than eighty known elements ; but the com- 

 pounds formed of them are innumerable. Carbon is found 

 in all substances formed by the growth of living things. 

 That there is carbon in sugar, for example, can easily be 

 shown by charring it on a hot shovel or a stove until its 

 water is driven off and only charcoal is left. Part of the 

 starch in a biscuit remains as charcoal when it has been 

 half burned. 



Oxygen and the Air. The great activity of pure oxygen 

 in attacking other substances can be shown by passing 

 into a fruit-jar a lighted splinter, a piece of Hghted mag- 

 nesium ribbon, an old watch spring (or a bit of picture 

 wire), the end of which has been dipped in sulfur and 

 lighted. About one fifth of the air is oxygen and about 

 four fifths is nitrogen and other inactive gases. Pure 

 nitrogen will quickly extinguish a lighted splinter thrust 

 into it. It is the oxygen in the air that supports all forms 

 of burning. Less than one half of one per cent of the 

 air is an inactive gas called carbon dioxid, a compound 

 of carbon and oxygen. It is formed not only when wood 

 or coal is burned, but also by the life processes of animals 

 and plants. 



Favorable and Unfavorable Conditions for Evaporation. 

 Pour the same quantity of water (half a glassful) into 

 three saucers and two bottles. Place one saucer near a 

 hot stove ; place the other two in a cool place, having first 

 covered one of them with a dish. Place one of the bottles 

 by the stove and the other by the remaining saucers. After 



