the cork. Place some bits of shaving in the tube, cork it, and make the
cork perfectly air-tight by coating it with bees wax or paraffine. Heat
the test-tube gently over an alcohol lamp. The wood turns black, and vapor
issues from the jet, which may be lighted (Fig. 4). Care should be taken
to expel all the air before lighting.

(6) That the burning hydrogen forms water by uniting with the oxygen of
the air, may be shown by holding a cold glass tumbler over the jet, or
over any flame. The glass will be dimmed by drops of moisture.

The charred part of the wood is charcoal, which is one form of carbon.
Our ordinary charcoal is made by driving off all the gases from wood, by
burning it under cover where only a little air can reach it. The volatile
gases burn more readily than the carbon, and are the first substances to
be driven off, so that the carbon is left behind nearly pure. In the same
way we have driven off all the gases from the half-burned match and left
the carbon. The teacher should have a piece of charcoal to show the
pupils. It still retains all the markings of the wood.

If the combustion is continued, the carbon also unites with the oxygen of
the air, till it is all converted into carbonic acid gas. This was the
case with the match where we left the glowing spark. The gray ash that was
left behind is the mineral matter contained in the wood.

(7) We can show that this gas is formed by pouring lime water into a
bottle in which a candle has been burned as in (2). The water becomes
milky from a fine white powder formed by the union of the carbonic acid
gas with the lime, forming carbonate of lime. This is a chemical test.

The wood of the match is plainly of vegetable origin; so also is the