While the oxyhydrogen flame is intensely hot, it is almost non-luminous. If directed against some infusible substance like ordinary lime (calcium oxide), the heat is so intense that the lime becomes incandescent and glows with a brilliant light. This is sometimes used as a source of light, under the name of Drummond or lime light.
Fig. 17
The blast lamp. A similar form of apparatus is commonly used in the laboratory as a source of heat under the name blast lamp (Fig. 17). This differs from the oxyhydrogen blowpipe only in the size of the tubes. In place of the hydrogen and oxygen the more accessible coal gas and air are respectively used. The former is composed largely of a mixture of free hydrogen and gaseous compounds of carbon and hydrogen. While the temperature of the flame is not so high as that of the oxyhydrogen blowpipe, it nevertheless suffices for most chemical operations carried out in the laboratory.
Uses of hydrogen. On account of its cost, hydrogen is but little used for commercial purposes. It is sometimes used as a material for the inflation of balloons, but usually the much cheaper coal gas is substituted for it. Even hot air is often used when the duration of ascension is very short. It has been used also as a source of heat and light in the oxyhydrogen blowpipe. Where the electric current is available, however, this form of apparatus has been displaced almost entirely by the electric light and electric furnace, which are much more economical and more powerful sources of light and heat.
EXERCISES
1. Will a definite weight of iron decompose an unlimited weight of steam?
2. Why is oxygen passed through the inner tube of the oxyhydrogen blowpipe rather than the outer?
3. In Fig. 14, will the flame remain at the mouth of the tube?
4. From Fig. 15, suggest a way for determining experimentally the quantity of water formed in the reaction.