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. 



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 

 some hours, examine the saucers and bottles and compare 

 and record the results. Explain. State three conditions 

 that are favorable to evaporation. State three ways in 

 which evaporation may be prevented or decreased. 



Tests for Acid, Alkaline, and Neutral Substances. For 

 acid tests, use sour buttermilk (which contains lactic acid), 

 or hydrochloric acid diluted in ten parts water, or strong 

 vinegar (which contains acetic acid}. Has the acid a char- 

 acteristic (" sour") odor and taste (test it only when very 

 dilute)? Rub dilute acid between the fingers; how does 

 it feel? Is there any effect on the fingers ? Obtain litmus 

 paper at a druggist's. Dip a strip of red litmus and of 

 blue litmus paper into the acid. What result ? 

 ' For alkaline tests, dissolve in a glass of water a spoonful 



