Hello guys I have ran across two equally great sites, the First is Le Guerre des Gaz (The War of Gases?) which deals with any thing you would like to know about Gas Warfare during the First World War. And the second one is Les mitrailleuses du premier conflit mondial (Machine-guns of the First World War) this is a great site, it has information on I believe every French and German Machine gun used. Unfortunately both sites are in French, but with Babel Fish you should be able to get the jest of the meaning.
I have a slightly morbid interest in the first site as gas (mustard) is what did for my maternal grandfather (Dublin Fusiliers 1914 -1918) although it took until the 1940s to actually finish him off.
I to have a slight fascination with GAS, not the actual gas itself, or how it kills and disables people, but how it was discharged. Like the Mortars used, and the pipes, cylinders etc, you see lying around in trenches.
I am also sorry that your Grandfather suffered so long with the effects of GAS, My Great Grandfather also suffered from the effects of mustard gas, my father tells me it was not a pretty site.
God Bless them both!! And God bless all the Men on all sides who died and suffered under such a horrible weapon