How was poisonous gas regarded before its use in ww1?

On April 22, 1915, German forces shock Allied soldiers along the western front by firing more than 150 tons of lethal chlorine gas against two French colonial divisions at Ypres, Belgium. This was the first major gas attack by the Germans, and it devastated the Allied line.

https://www.history.com/this-day-in-history/germans-introduce-poison-gas

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b.provides a written record of the transaction