n Englishman, in 1860, and
rediscovered by a German chemist, Victor Meyer, in 1886, but he found it
so dangerous to work with that he abandoned the investigation. Nobody
else cared to take it up, for nobody could see any use for it. So it
remained in innocuous desuetude, a mere name in "Beilstein's
Dictionary," together with the thousands of other organic compounds that
have been invented and never utilized. But on July 12, 1917, the British
holding the line at Ypres were besprinkled with this villainous
substance. Its success was so great that the Germans henceforth made it
their main reliance and soon the Allies followed suit. In one offensive
of ten days the Germans are said to have used a million shells
containing 2500 tons of mustard gas.

The making of so dangerous a compound on a large scale was one of the
most difficult tasks set before the chemists of this and other
countries, yet it was successfully solved. The raw materials are
chlorine, alcohol and sulfur. The alcohol is passed with steam through
a vertical iron tube filled with kaolin and heated. This converts the
alcohol into a gas known as ethylene (C_{2}H_{4}). Passing a stream of
chlorine gas into a tank of melted sulfur produces sulfur monochloride
and this treated with the ethylene makes the "mustard." The final
reaction was carried on at the Edgewood Arsenal in seven airtight tanks
or "reactors," each having a capacity of 30,000 pounds. The ethylene gas
being led into the tank and distributed through the liquid sulfur
chloride by porous blocks or fine nozzles, the two chemicals combined to
form what is officially named "di-chlor-di-ethyl-sulfide"
(ClC_{2}H_{4}SC_{2}H_{4}Cl). This, however, is too big a mouthful, so
even the chemists were glad to fall in with the commonalty and call it
"mustard gas."

The effectiveness of "mustard" depends upon its persistence. It is a
stable liquid, evaporating slowly and not easily decomposed. It lingers
about trenches and dugouts and impregnates soil and cloth for days. Gas
masks do not afford complete protection, for even if they are
impenetrable they must be taken off some time and the gas lies in wait
for that time. In some cases the masks were worn continuously for twelve
hours after the attack, but when they were removed the soldiers were
overpowered by the poison. A place may seem to be free from it but when
the sun heats up the ground the liquid volatilizes and the vapor soaks
through the clothing. As the