86 SCIOPTICON MANUAL. 



the tank, put in it a strip of sheet zinc, and long leaf- 

 like blades of metallic tin will at once be seen to shoot 

 out in all directions. 



Experiment 5th. Make a concentrated solution of 

 crystals of urea in alcohol of about 95 per cent. (The 

 common 85 per cent^ alcohol will not answer.) Let a 

 few drops of this fall on a glass plate, and with the 

 finger spread it rapidly over the surface, and then at 

 once place it as an object in the lantern. After about a 

 minute, blow gently on the plate with a bellows (not 

 with the breath), and at once on the screen will be seen 

 the growth as of frost crystals shooting over the field 

 in all directions. 



Experiment 6th. If sulphate of copper in solution is 

 mixed with enough gum-arabic water to make the solu- 

 tion form a continuous film, when flowed like collodion 

 on a clean glass, and such plates are allowed to dry 

 slowly in a nearly horizontal position, a very beautiful 

 crystalline vegetation will set in, which varies in its 

 character with the proportion of gum used, and will 

 make objects well fitted for exhibition with the lantern. 



In place of sulphate of copper, we may use nitre, or 

 ferrocyanide of potassium, with the production of an 

 entirely new class of forms. 



By placing the plates so covered with crystals over a 

 leaden dish, in which is a little fluor-spar, moistened 

 with sulphuric acid, and warmed slightly (giving off 

 fumes of hydrofluoric acid), permanent etchings may bo 

 prepared, which are also very beautiful objects for the 

 lantern. 



These are only a few of the experiments of this char- 

 acter which can be performed with the lantern, but they 

 will indicate the direction in which each one can be a 

 discoverer and inventor for himself. 



