Curtis and Harvey's rifle powder was very highly regarded right up until the company ceased production. Far from occasioning your visit to hospital, it will be right up there quality-wise with present-day Swiss powder, of that there is no doubt. Bill Curtis, bastion of BP shooting in the UK and curator and general maven of all things relating to the Crimean War, and presently the incumbent source of all knowledge in the Royal Armouries, is, I believe, a great nephew of the Curtis of that company name.
Treat it as gold-dust, since there will never be any more, and deal with it as though it was Swiss in terms of loads.
Enjoy it on my behalf.
With envy - tac