342 PHOTOGRAPHIC FACTS AND FORMULAS 
oxide 5; magnesium 2.5, cerium oxalate 0.5, manganese oxide 
0.25. The chromates or tungstates of thorium may also be 
used, and the mixtures keep well and give little smoke, such 
as magnesium 1, thorium chromate 2. Lumiére patented the 
use of the chromates of iron, manganese, chromium, nickel, 
cobalt, aluminium, cerium, lead, copper and antimony, as 
giving little smoke. Boric and silicic acid have also been 
patented when added in equal quantity to the magnesium, and 
these mixtures are non-explosive, give little smoke and almost 
as much light as the permanganate mixtures. 
Aluminium may be used in place of magnesium, but it does 
not give quite so actinic a light. It may also be mixed with 
magnesium. A slow-burning aluminium mixture is alu- 
minium 6, potassium nitrate 6, barium nitrate 6, dextrine 2, 
sulphur 1. The aluminium powder is sometimes greasy and 
clumps together ; in this case, it should be mixed with benzole, 
petroleum ether, gasoline, or as these are dangerous, carbon 
tetrachloride may be used. The mixture should be well 
shaken, the powder allowed to settle, the liquid poured off, 
and the powder allowed to dry. 
AMOUNT OF FLASHLIGHT PowpER NEEDED.—Orostini 
gives the following table of the quantity of magnesium and 
stop to be used: 
Distance of object Quantity of magnesium in grams 
from light Rey, 7:90 filo false 
1 meter 0.07 0.01 0.2 0.4 0.8 
2 meters 0.28 0.04 0.8 1.6 a2 
3 meters 0.63 0.09 1.8 3.6 72 
4 meters (Pvt 1.06 32 64 128 
MAGNESIUM FOR UNDERGROUND Worxk.—Martel divides 
the subjects into two classes: (1) short distances from 15 
to 20 meters, and (2) long distances from 15 to 60 meters. 
For the shorter distances he recommends three or four strips 
