And, see, if it had actually been the sugar, and it had been part of some complicated plot on the part of Doctor Mortimer or something, and Sherlock had reason to believe it was the sugar, that might even have been clever. But when it wasn't actually the sugar, I just have to go what.

I'm pretty sure Sherlock didn't spray the gas around himself; I went back and re-watched the scene. But. Yeah. It makes no sense either way.