LIGHT. 121 



inches long. Now hold a stick of glass like a large glass 

 stirring rod in the flame at the same place when the 

 lime cylinder is fixed: It will glow brilliantly with 

 nearly the monochromatic light of sodium, and if the 

 prism is in its place the bright yellow line indicative of 

 that element will appear upon the screen. The glass 

 will need to be turned slowly, and the attention of one 

 person will be needed constantly to keep it in place. 

 Sticks of soda glass may be had in the market, made 

 especially for projecting the sodium line in this way, 

 but the -spectrum can be obtained from almost any 

 piece of glass. 



Another good method is to soak soft-pine sticks six 

 or eight inches long and half an inch thick in saturated 

 solutions of the chlorides of the various elements to be 

 projected, as the chlorides are more volatile than other 

 salts. Let the sticks remain in these solutions several 

 days before they are to be used, as a much larger 

 quantity of the material will be absorbed. These 

 solutions may conveniently be made in test tubes six 

 or eight inches long, remembering to label each tube 

 by pasting a bit of paper upon it and writing the symbol 

 of the substance contained in it. The chlorides of all 

 the substances named above may be prepared in this 

 way and a stick provided for each one. 



The saturated and still wet stick must be put imme- 

 diately into the flame where the glass and the lime 

 cylinder are otherwise placed, and, holding one end in 

 the hand, keep turning it slowly. The stick will glow 

 and give out the kind of light that is peculiar to the 

 included element. 



The spectrum consisting of bright lines will be 

 quite bright and sufficiently large to be plainly seen by 

 an audience of a thousand persons. Sodium, Calcium, 



