Klrai. School Leaflet. 695 



posed of these two gases is because the gases have been combined and 

 formed water and because water has so often been separated into the two 

 gases. Any such substance is called a compound. 



All living things are made up of different compounds of elements. 

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

 oxygen. Flour is composed of starch and of other compounds contain- 

 ing nitrogen, phosphorus, potassium, and others. 



Only a few of the seventy elements are necessary for the growth of 

 plants and animals. The following elements are commonly found in 

 plants and the first ten are absolutely necessary for plant growth : oxygen, 

 hydrogen, carbon, nitrogen, iron, potassium, phosphorus, calcium, sulfur, 

 magnesium, sodium, chlorine and silicon. 



Oxygen, hydrogen, and nitrogen are all invisible gases so that we 

 do not see them. Air is mostly a mixture of oxygen and nitrogen so 

 that we know it even if it is invisible. Iron and sulfur occur as ele- 

 ments. Calcium is not ordinarily seen, but cjuick lime is either calcium 

 or magnesium combined with oxygen. Of course the calcium looks very 

 differently from lime. Silicon and oxygen combined make up the larger 

 part of sand. Salt is a compound of sodium and chlorine. 



A green plant is mostly water, often nine-tenths water. Of the other 

 substances, carbon makes up nearly half, nitrogen comes next and there 

 are smaller amounts of the other elements. 



No plant can grow if any one of the first ten elements mentioned is 

 lacking, but since the soil furnishes an abundance of iron, sulfur, magne- 

 sium, sodium, chlorine and silicon, a farmer does not need to give special 

 attention to these elements. The carbon dioxid of the air furnishes 

 carbon. Water furnishes hydrogen and oxygen. The remaining ele- 

 ments — nitrogen, potassium, phosphorus and calcium — • are often insuffi- 

 cient in the soil for the production of a good crop, so that these, particu- 

 larly the first three, are the elements that farmers buy in fertilizers. 



If the school is connected with a high school it wnll be well to have 

 some nitrogen, hydrogen, and oxygen prepared for the class to study. 

 The high school chemistry tells how to do this. 



Words to be spelled and defined. 



Element, a substance that cannot be separated into other things. 



Compound, a union or two or more elements — a. substance that can 

 be separated into two or more things or substances. 



Nitrogen, an invisible gas that constitutes about four-fifths of the 

 atmosphere. 



Oxygen, an invisible gas that constitutes about one-fifth of the at- 

 mosphere. 



Carbon dioxid, a compound of oxygen and carbon, sometimes called 

 carbonic acid gas. Tt is present in small quantity in the atmosphere, and 



