Bunsen burner, heat-proof mat.
Metal tray such as a large tea tray.
The quantities given are for one demonstration.
10g of ammonium dichromate (VI).
A little ethanol.
One piece of blue cobalt chloride paper.
Access to a fume cupboard.
Working in a fume cupboard, place a conical pile of about 10g of
ammonium dichromate on a heat-proof mat standing on a tray to collect
the chromium oxide that shoots into the air. Soak about a 3cm length
of wooden spill in ethanol and stick this into the top of the pile
so that about 2cm protrudes to act as a wick. Light the wick.
As the wick burns down into the ammonium dichromate, the compound
begins to spark and decompose leaving behind a cone of green chromium
(III) oxide that has a considerably larger volume than the original
compound. Some of this oxide shoots into the air.
The 'volcano' burns for between 30 seconds and one minute. Hold
a watch glass above the 'volcano'; this becomes steamed up with
water from the decomposition. Confirm that this is water with blue
cobalt chloride paper.
The reaction may also be started by pointing a roaring Bunsen flame
at the top of the pile of ammonium dichromate.