© International Film Service
GERMANS STARTING A GAS ATTACK ON THE RUSSIAN LINES
Behind the cylinders from which the gas streams are seen three lines of German troops waiting to attack. The photograph was taken from above by a Russian airman
© Press Illustrating Service
FILLING THE CANNISTERS OF GAS MASKS WITH CHARCOAL MADE FROM FRUIT PITS IN LONG ISLAND CITY
Because free chlorine would not stay put and was dependent on the favor of the wind for its effect, it was later employed, not as an elemental gas, but in some volatile liquid that could be fired in a shell and so released at any particular point far back of the front trenches.
The most commonly used of these compounds was phosgene, which, as the reader can see by inspection of its formula, COCl2, consists of chlorine (Cl) combined with carbon monoxide (CO), the cause of deaths from illuminating gas. These two poisonous gases, chlorine and carbon monoxide, when mixed together, will not readily unite, but if a ray of sunlight falls upon the mixture they combine at once. For this reason John Davy, who discovered the compound over a hundred years ago, named it phosgene, that is, "produced by light." The same roots recur in hydrogen, so named because it is "produced from water," and phosphorus, because it is a "light-bearer."