By World War II there were a variety of different gasses that could be used against troops and civilian populations, some were lacrimatory gasses that induced tears and incapacitated a soldier by temporarily preventing him from seeing, others were vesicants which produced terrible chemical burns whilst others prevented a soldier from breathing properly. Different gasses needed different methods of prevention- vesicant gasses required exposed skin to be covered whilst for other gasses, just donning a gas mask was sufficient. As such it was essential for troops to be able to identify what gas was being used against them and smell was the simplest indicator. Each gas had distinctive smells and various methods were used to teach soldiers what these were so they could quickly identify what had been used.
Short mnemonic poems have long been used in schools to help children learn small pieces of information- many of us remember learning the colours of the rainbow by reciting ‘Richard Of York Gave Battle In Vain’- and today we are looking at a small printed slip of paper with a poem to remember the properties of different gases:
This is quite a long poem, so one wonders just how effective it might have been, but it seems the authorities were willing to try all and every method of getting the different indicators of gasses into the heads of their men. How a man would manage to recite the whole poem under stress when a man had split seconds to take a course of action is unclear, but happily gas was never used to this became an unnecessary precaution.
Tales from the Supply Depot 
Nasty stuff, some of the more persistent types are still being brought up today from long buried shell holes from WW2, WW1 and the ones before, the amount of ordnance dug up by farming and frost heaves is substantial. This area luckily doesn’t get much of that, although the odd bit washed up on shore from time to time, we had to deal with a WW2 torpedo and occasionally stuff gets dredged in various ways. I even got a call for a dug-up cannonball from the 1700’s, luckily it was solid shot and not a mortar, although the blackpowder filler would in all probability have gone inert, there’s always the chance it might have stayed dry and precautions still have to be taken as if it were brand new.
In parts of Continental Europe there are dedicated EOD teams who make the rounds in plowing season to pick up the winter’s ‘gifts’ and deal with anything found during excavations.
Vesicants like Lewisite or ‘mustard’ are particularly long lived and a constant danger when you’re gathering rusty lumps of what vaguely look like artillery shells but could have anything inside from sensitized decomposing fillers to chemical agents.
It’s been said that every shovelful could break into a pocket of gas that’s been sitting there for over a century now but still potent, the odds are pretty low but never zero.