Unusual gunpowder flask

[Kmaddock]

Thanks Corrado
Am I correct in the Sheffield atributation?
Also have you ever seen a similar mechanism for powder dispensing.
I assume it was designed so that you did not have to put your thumb over the top of the spout, probably something a gentleman should not have to do to getting his thumb dirty.
But quiet a complex solution to a simple operation.
Regards
Ken