UNITED STATES WEATHER SERVICE 335 



sufficient potassium permanganate solution to color the 

 water. Heat gently to the boiling point. If the color 

 changes to a brownish tint, it indicates the presence of 

 organic matter. 



2. Test for chlorides : 



To a test-tube half full of water, add a few drops of 

 nitric acid, and then a few drops of silver nitrate solu- 

 tion. If there is any cloudiness, it shows that the water 

 had traces of chlorides in it. 



3. Test for sulphates : 



To a test-tube half full of water add a few drops of 

 barium chloride solution. If there is a whitish precipitate, 

 it indicates the presence of sulphates in the water. 



4. Test for lime compounds: 



To a test-tube half full of water add a few drops of 

 fresh solution of ammonium oxalate. A white precipitate 

 indicates the presence of calcium or lime compounds. 



As a note-book record of this lesson, the pupils should 

 write an essay on the Water Supply, bringing out the 

 facts they have learned, and showing the attitude they 

 have toward the subject. 



LESSON XCVII 



THE UNITED STATES WEATHER SERVICE 



Farmers dependent upon weather. There is no sub- 

 ject of more vital interest to the farmer than the weather. 

 Especially is this true in the month of August In the 

 corn belt the condition of the weather either makes or 

 mars the crop. As the rain falls "on the just and on the 



