How toxic gas was deployed in WWI

[D]uring the night the German enemy forces crawled with metal and glass canisters of the poison gas to the very front of the Russian lines, or at least to the outer edges of the barbed wire perimeter.  The crawler would retreat, and then the whole of the attacking force would wait until daylight and a favorable wind condition at which time riflemen would discharge at the canister, a direct hit mixing the contents of the vials, producing the desired gas.  The wind would then pick up the gas and disperse it, the Germans waiting for the first leg of their attack to take effect on the poor soldiers in the trenches, and then attack once the gas had mostly cleared.