158 THE ART OF PROJECTING. 



To water made slightly acid, add enough litmus 

 solution to turn it red and project it ; then drop a lump 

 of carbonate of ammonia into it. It will dissolve 

 rapidly with effervescence, and the solution will be 

 made blue about the crystal, and if there is enough of 

 it the whole solution will ultimately become blue. 



The gradual solution of substances in water may be 

 nicely shown by filling the tank with pure water and 

 dropping a crystal of alum or sulphate of zinc or sul- 

 phate of copper into it. Where the substance is dis- 

 solved the solution will be denser, and its refractive 

 powers changed, which will be manifest by gently stir- 

 ring it with a glass rod. 



A dilute solution of copper sulphate may be placed 

 in the tank. With a pipette, force into the solution 

 some ammonia water: A dense precipitate will at first 

 be formed, which will afterwards be dissolved if am- 

 monia enough has been added, leaving the solution a 

 beautiful blue color. A few drops of sulphuric acid 

 will reproduce the precipitate and destroy the color ; 

 and when the solution again becomes clear, a few drops 

 of ferrocyanide of potassium added will produce a 

 brownish-red bulky precipitate, which will present a 

 fine appearance upon the screen. 



In like manner all of the characteristic reactions of 

 inorganic chemistry may be projected, and often with 

 much less expenditure of materials than would be used 

 if large vessels were employed to demonstrate the 

 same things. One who has projected a number of 

 these phenomena will find no difficulty in projecting 

 any reaction that may be observed in a test-tube. 



Pictures of chemical apparatus, of processes, etc., 

 will be very convenient for projection when instruction 

 is given in chemistry. 



