44 THE ART OF PROJECTING, 



porte lumiere will be reflected upward through the two 

 lenses upon another smaller mirror, «, which may be 

 held in a retort-stand, and the beam directed to the 

 proper place. 



PHYSICAL EXPERIMENTS. 



DIVISIBILITY OF MATTER. 



A good way to show the minute divisibility of matter 

 is to dissolve, in water, a small quantity, say a gram, of 

 cupric sulphate, and add enough ammonia-water to 

 make a clear, blue solution. Put it into the chemical 

 tank, having measured its capacity in cubic centimeters, 

 or inches, fill it with water, and project the tank by the 

 method described on page 183. A beautiful blue color 

 will appear upon the screen. With a small syphon of 

 bent-glass tube, draw out one-half of the solution and 

 fill up with pure water. The amount of coloring mat- 

 ter will be reduced one-half, but the solution will be 

 strongly colored. Remove, in the same way, another 

 half, and so on until the blue color is no longer visible 

 — comparing the color with that of pure water, pro- 

 jected, at the same time, in a test-tube. Keep account 

 of the number of dilutions, and at last, when the blue 

 color is on the vanishing point, calculate the weight of 

 cupric sulphate in each cubic centimeter of water. In 

 place of the copper solution, any of the analine dyes 

 will do as well. 



The same thing can be illustrated with a soap-bubble, 



