Experiment 24.--Fill a tube 2 or 3 cm. in diameter with calcium
chloride, CaCl2, and connect one end with a generator of H (Fig.
15). At the other end have a philosopher's lamp-tube.Observing
the usual precautions, light the gas and hold over it a receiver,
till quite a quantity of moisture collects. All water was taken
from the gas by the dryer, CaCl2. What is, therefore, the product
of burning H in air? Complete this equation and explain it: 2H +
O = ? Figure 16 shows a drying apparatus arranged to hold CaCl2.

[Fig. 15][Fig. 16]

37. Explosiveness of H.

Experiment 25. -- Fill a soda-water bottle of thick glass with
water, invert it in a pneumatic trough, and collect not over 1/4
full of H. Now remove the bottle, still inverted, letting air in
to fill the other 3/4. Mix the air and H by covering the mouth of
the bottle with the hand, and shaking well; then hold the mouth
of the bottle, slightly inclined, in a flame. Explain the
explosion which follows. If 3/4 was air, what part was O? What
use did the N serve? Note any danger in exploding H mixed with
pure O. What proportions of O and H by volume would be most
dangerously explosive? What proportion by weight?

By the rapid union of the two elements, the high temperature
suddenly expanded the gaseous product, which immediately
contracted; both expansion and contraction produced the noise of
explosion.