144 LESSONS IN 



No one has been able to separate them into different 

 things. Gold cannot be separated into anything but 

 gold. For centuries men tried to make gold out of other 

 things, but they failed. Water is not an element; it is 

 a compound. A chemist can separate it into two gases, 

 hydrogen and oxygen. 



Elements and compounds. All living things are 

 made up of different compounds of elements. The 

 starch of corn is a compound of carbon, hydrogen, and 

 oxygen. Only a few of the eighty elements are neces- 

 sary for the growth of plants and animals. The follow- 

 ing elements are commonly found in plants, and the first 

 ten are absolutely necessary for good plant growth : 

 oxygen, hydrogen, carbon, nitrogen, iron, potassium, 

 phosphorus, calcium, sulphur, magnesium, sodium, chlo- 

 rine, and silicon. Oxygen, hydrogen, and nitrogen are 

 invisible gases, so we do not see them. Gold and sul- 

 phur occur as free elements. Calcium is not ordinarily 

 seen, but ordinary quicklime is either calcium or mag- 

 nesium combined with oxygen. Silicon and oxygen 

 combined make up the large part of sand. Salt is a 

 compound of sodium and chlorine. A green plant is 

 mostly water. Of the other substances, carbon makes 

 up nearly one-half; nitrogen comes next; and there are 

 smaller amounts of other elements. 



Essential elements for plants. No plant can grow 

 unless supplied with the first ten elements mentioned 

 above. The soil furnishes iron, sulphur, magnesium, 

 sodium, chlorine, and silicon; a farmer does not need 

 to give special attention to these. The carbon dioxide 



