340 PHOTOGRAPHIC FACTS AND FORMULAS 
formed. Evaporate until dry, dry for some time at 105° C. 
(220° F.), and reduce to powder. Lithium carbonate, 1; 
alone with magnesium or mixed with one of the above, gives 
a red light. Potassium permanganate, 1.3; does not explode 
when struck ; gives brown smoke and more sparks than others. 
Manganese dioxide, 1; should be very finely powdered. Per- 
fectly safe, burns fairly rapidly with little smoke. 
CHLORATES, PERCHLORATES, ETC.—Potassium chlorate, 2 
or 1; must be powdered. Potassium perchlorate, 2; also in 
powder. Sometimes a mixture of the two is used, as chlorate, 
34, perchlorate, 34. Both the salts must be in fine powder 
before mixing, and should preferably be mixed with a feather 
on a sheet of paper, as strong friction is apt to cause an 
explosion. These compounds cannot be sent through the 
post. Potassium or ammonium persulphate, 2. Potassium 
or ammonium bichromate, 2; burns rather slowly. Chrome 
alum, anhydrous, 1; a perfectly safe mixture. 
FLasH SHEETS.—Flash sheets may be prepared by sus- 
pending magnesium powder in celluloid or pyroxyline solu- 
tion, casting on glass and stripping before quite dry. The 
following mixture has also been proposed: 
Magnesium 1 part 
Potassium chlorate 2 parts 
Celluloid varnish 3 parts 
To be used in the same way. Another method proposed is to 
coat paper with starch paste, rub magnesium powder into it, 
and dry. Thin blotting paper, soaked in solution of potas- 
sium bichromate and dried, is thus pasted and dried. 
FLasH CanbDLEs.—Slow-burning mixtures can easily be 
made, and the so-called time-light candles are small tubes of 
paper, impregnated either with pyroxyline solution or potas- 
sium nitrate, and filled with a magnesium compound. Or 
the containers may be made of thin aluminium foil, 0.1 to 
