Item 03: John Duncan McRae diary, 10 February-6 May 1917 - Page 46

[Page 46]

of effects of a gas attack.

Gas is a very potent opponent in the field unless full preventative measures are take; if such measures are taken it can do no harm.

Chlorine seems to be the most powerful gas used. It is packed in liquid form in large metal cylinders and is also used in "gas-shells". Chlorine is so strong & poisonous that even when mixed with air in the proportion 1/10,000 it proves fatal if inhaled. Thus with a fair breeze it will kill 10 miles behind the point of attack & its effects have been felt up to fifteen miles away.

To nullify gas effects helmets or box respirators are worn. The helmet is made of a double thickness of flannelette with eye-glasses & mouthpiece, the latter being provided with a valve. The helmet is soaked in certain chemicals