THE ATMOSPHERE. 175 



Examine a bit of granite or gneiss with a lens. How many 

 kinds of minerals can you see? Break it up with a hammer. 

 Pick out bits of mica ; of feldspar. The feldspar is the source 

 of clay. "What becomes of the disintegrated quartz 1 



Powder a bit of limestone and place in a bottle or test-tube. 

 Add some dilute hydrochloric acid. Note the effervescence. 

 Use dilute sulphuric acid, also strong vinegar, and compare 

 the results obtained in the three cases. Apply heat and note 

 effects if any. Experiment similarly with slate, gypsum, 

 egg-shells, quartz, clay, marble. Select the substances con- 

 taining lime. 



If the school is equipped with the means of using a Bunsen 

 burner, or even a blowpipe with a grease-lamp, the number of 

 interesting experiments upon and tests of minerals and rocks 

 may be much enlarged. Crosby's " Determination of Minerals," 

 106 pages, will be found a helpful book. 



The Atmosphere. — In most public schools the means of 

 teaching the composition of air by the Nature Study method 

 will not be available. Lavoisier's experiment of separating 

 the gases and investigating each separately can be repeated in 

 a small laboratory, but the steps would hardly be understood 

 by pupils at this stage. It may be shown by burning a 

 candle in an inverted gem jar over water, still better by 

 supporting a piece of phosphorus in a similarly inverted jar 

 for a few hours, that about one-fifth of the air in the jar has 

 been displaced by water. The pupils may be told that the 

 fifth that combined with the phosphorus is called oxygen and 

 that it is the life-giving, flame-supporting element of the 

 atmosphere, and that the remainder is mostly nitrogen. A 

 fraction, four ten-thousandths, is carbon dioxide, which 

 though small is very important because it is necessary for 

 plant food. There is always some water-vapor in the air. It 

 has important uses, too, one of them being to equalize and 

 distribute heat. 



