b. Northern lights. 



Experiment 35. Electric glow from 

 sugar and from paper. 



WATER. VIII. 



42. A brief summary of the facts stated under the 

 same topic in the work for the fifth, sixth, and 



seventh grades. 



43. Hard water. 



a. Temporary hardness. 



Experiment 36. The cause of temporary 

 hardness. 



Experiment 37. Stalactites and stalag- 

 mites. 



b. Permanent hardness. 



Experiment 38. To measure permanent 

 hardness. 



44. Precipitation. (See Section 88.) 



Experiment 39. Precipitation. 

 AS. Purification of water. 



a. Removal of bacteria. 



b. Removal of other plants. 



46. Acids and bases. (See Sections 89, 90, and 91.) 



a. Tests. 



Experiment 40. Testing acids and bases. 

 1). Neutralization. 



Experiment 41. Neutralization mikes a 

 salt. 



47. Salts. 



a. Efflorescent salts. 



Experiment 42. Efflorescent salts. 



