ELEMENTARY PHOTO-MICROGRAPHY. 129 



Uranium nitrate . . . . 6 grains. 



Potass, ferricyanide . . 5 



Acetic acid . . . . . . i drop. 



Water . . . . . . i ounce. 



Dissolved in the order given. The slide must 

 be quite free from hypo before treatment. Wash 

 and then immerse in one ounce water in which 

 five grains ferric chloride are dissolved. 

 Again wash and dry. 



The " Tabloid " toners by Burroughs and 

 Wellcome are very convenient and easy to use. 



RULE FOR FINDING DISTANCE OF LANTERN 

 FROM SCREEN. 



Add one to the number of times the slide is 

 to be enlarged, and multiply by the focus of lens 

 in inches. The answer will be in inches. 



EXAMPLE : What distance should lantern, with 

 Sin. focus lens, be from screen to give a loft, 

 picture ? 



If the lantern slide has a clear opening of sin., 

 then the magnification of a loft, picture would 

 be forty times. Therefore (40 + 1) x 8 = 328in., 

 or 27ft. 4in. 



