SCIOPTICON MANUAL. 85 



of copper, and mix it well with the water of the tank, 

 then with the pipette run in, with more or less force, 

 some diluted ammonia, pausing from time to time to 

 observe the progress of the effect. On the screen will 

 be observed the gathering of a tempest of black storm- 

 clouds, which twirl around in violent commotion, as if 

 urged by a tornado of wind, but as the action continues, 

 these clouds will melt away, and leave the entire field 

 of a serene and beautiful sky-blue. 



By now throwing in some diluted sulphuric acid, the 

 same changes can be reproduced, and so on alternately 

 for a number of times. Then when the tank is clear, 

 with an excess of acid, let fall a few drops of a solution 

 of ferrocyanide of potassium from a small pipette, and 

 rich red curdled clouds of ferrocyanide of copper will 

 form with a beautiful appearance. 



Experiment 2d. Having rinsed the tank, or taken a 

 fresh one with water in it as before, add to this some 

 solution of litmus, until the whole acquires a purplish- 

 blue tint. Now throw in very gently a little very dilute 

 acid, and allow it to diffuse. On the screen will appear 

 the image of a beautiful sunset sky, with its changing 

 tints of drifting clouds. 



When all has changed to red, add ammonia, and so 

 reverse the change, which may then be repeated. 



Experiment 3d. Proceed exactly as in the last case, 

 but with a solution of cochineal in place of litmus. The 

 red color will then be changed by the acid to a brilliant 

 yellow, and by ammonia to a rich purple. 



Experiment 4th. Into a tank of water drop slowly a 

 strong solution of the acid perchloride of tin. This 

 on the screen will resemble the eruption of a submarine 

 volcano. 



When a pretty strong solution has thus been made in 



