§ Mr. C. Wilsonasked the Home Secretary whether he can explain the terms true gas, persistent gas and contaminating gas, and give a list of each?
§ Mr. Lloyd:The term "gas" in warfare means any chemical substance, whether solid, liquid or vapour, which is used because it produces poisonous or irritant effects upon the human body. A "true gas" is a substance which is gaseous at ordinary temperatures. A "persistent gas" is usually a liquid at ordinary temperatures but evaporates slowly, giving off dangerous vapour. A "contaminating gas" is one which remains on an object or person and necessitates special treatment for the removal of it.
The best known examples are:
True gases—chlorine. phosgene.
Persistent gases—mustard gas. many lachrymatory gases.
Contaminating gases—mustard gas. lewisite.
Particulars regarding each of these gases will be found in the Air-Raid Precautions Handbook No. 1.