Knapsack Sprayers
Knapsack sprayers are issued for use to clear gases out of the trenches after the cloud has blown over. A man with the sprayer on his back (and wearing his smoke helmet) slowly traverses the trench, working the spray. If this is not done the heavy poisonous gas may linger in the trench for days and be a source of great danger.
If supports or reinforcements enter a trench charged with gas, they should be preceded by a man using a sprayer.
Sprayers are charged with sodium thiosulphate—more commonly known as "hypo"—6 pounds being dissolved in a bucket of water and a handful of ordinary washing soda added.
Garden syringes and buckets may be used if sprayers are not available, but these are not so effective. Sprayers should be charged before they are taken up to the trenches, and should be kept ready for immediate use.
Every officer defending a trench against an enemy gas attack should endeavor to collect information whenever possible, to be sent to headquarters through the usual channels. Particularly valuable is the capture of apparatus used by the enemy either for disseminating gas or for protection against it. If a shell attack is made, unexploded shells or portions of them should be sent through to headquarters at once. The time of day, duration of attack, color, taste or smell of gas used, effect on the eyes, breathing, and all other symptoms should be noted. New gases may be used at any time, and speedy information greatly forwards the adoption of preventive measures.
CHAPTER X
Service in the Trenches