JR North fired this volley in news:gPWdncarTqmW3bzRnZ2dnUVZ firstname.lastname@example.org:
You're thinking of Candy fuel. Zn/S heated to the temperature that will fuse the sulfur will start to react immediately -- injuring you.
There are solvents that will dissolve sulfur, but the traditional way to treat Zn/S so it will not break up during thrust is to VERY slightly dampen it with a tiny bit of alcohol (just for processing, to keep down the dust), then pressing it under hydraulics to about 6800 psi on the composition (which makes the sulfur go amorphous, acting as if it had dissolved, but at a much lower temperature). When it dries completely, which takes weeks, it becomes a solid grain than can be lightly machined, and will not break up easily.
But --- WHY? Zn/S has one of the lowest impulse figures of any fuel available. APCP is a strong fuel, inexpensive, easy to make, and fun to shoot.
Despite what a prior poster said, it's NOT "difficult to light". It burns like Hell's Fury with the mere touch of a match. But it was accurate to say it doesn't function by exploding, and has a shallower P/R curve, so it doesn't run away in a casing as easily as some other sorts of propellants.