What does this chart relate to?

[WATU]

Hi A light-hearted post to see how quickly someone can answer this. Attached is a page from a UK National Archives AIR file from mid-1941. As it says it relates to a Blenheim but other aircraft have similar charts including the Lysander. What munition does the chart relate to?

 

[WATU]

It is the predicted spread of gas from an aircraft-borne spray cannister. Scary stuff. Here is the full page.