For fictional use, I'd like to "construct" a clockwork device featuring phosphorus which could reasonably be expected to:
A) glow consistently.
B) explode upon some trigger (e.g., influx of air, mixture with another chemical, a spark), with enough explosive force or incendiary strength to kill someone standing very close.
1) this takes place in the early 18th century, so phosphorus has been discovered, but most of the modern types of phosphorus used in weaponry have not.
2) the quantity is no larger than a couple of liters.
I've read the relevant chapters in Emsley's 13th Element, and then moved on to the primary sources for the time – mostly records of demonstrations held for the Royal Society and Boyle's Aerial Noctiluca. It's hard to tell exactly what sort of phosphorus any of these early chemists were working with, but it looks like I can achieve goal (A) by just letting in a bit of air now and then (based on Boyle's description / Wikipedia on oxidation).
Goal (B) is more difficult. Is just oxygen enough?
Slare added sulfuric acid ("oil of vitriol") and achieved something, but it doesn't seem to have been an explosion exactly:
being well shiken together did first heat, and then throw up such fiery Balls, which like so many stars will adhere to the sides of the Glass and continue to burn for some time