What chemical available in 18th century would explosively react with phosphorus? 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.

Constraints:

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.

Progress:

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
I think if you just add oxygen you'll just end up with a lump of burning phosphorus. I would suggest having a timed explosive charge at the centre of a phosphorus payload to essentially achieve something like a white phosphorus bomb.

Since white phosphorus is pyrophoric, you only need to disperse it for it to ignite. To do this, you could either use an automated striking mechanism to ignite a fuse to something like black powder, or my Improvised Munitions Handbook suggests a combination sulfuric acid/potassium chlorate or perchlorate (note: not chloride) + sugar device, with the mechanism keeping the two components separate, would be suitable. 

The main problem with your design specifications as I see them is having an excuse to have the external surface of phosphorus exposed to the air: white phosphorus will only glow from the air-exposed surface, so if you put it behind glass, for example, it won't glow. A fine wire mesh as your external covering might do the job, but I'm not sure exactly what effect that has on reliability or effectiveness (and may cause the device to spontaneously and accidentally catch fire, especially if not packed properly).

Near explosion + being covered in burning white phosphorus = much sadness, probable death. See: White Phosphorus - Effect on People.

(Usual disclaimer: I am not a munitions designer.)