Page:Popular Science Monthly Volume 84.djvu/223

Rh and oxygen are exploded and the water formed is weighed or the amount of each gas used is measured. Also water is decomposed by electrolysis and the hydrogen and oxygen thus formed (the only things formed) are measured.

The heat given off in the combination of the gases is enormous, indeed, it is the most exothermic of all chemical reactions, 67,500 calories or heat units being evolved in the combination of 16 grams of oxygen with 2.016 grams of hydrogen—a calorie is that amount of heat which will raise one gram of water 1 degree centigrade. In the absence of indifferent gases, or an excess of one of the reacting gases, the reaction is not only so violent as to raise the gases to the combination temperature, 2,000° C, but to carry them beyond to 2,844° C, at which temperature only about one third of the gases combine, the remainder doing so gradually as the temperature falls. Almost any non-reactive (catalytic), highly heated substance, such as platinum sponge, or wire, stone, porcelain, glass, etc., will bring about a combination.

An oxy-hydrogen blowpipe is an arrangement for utilizing this heat energy, by bringing the two gases together in such a way that they will produce a sharp, intensely hot flame. The apparatus is so fashioned that the gases are conducted separately through the exit where they are to be lighted, thus avoiding any possibility of explosion, which otherwise takes place, if they are mixed. By means of such a flame, a temperature of 2,000° C. can be obtained.

Having learned that water (at least in the form of its components) is older than even the earth itself, that its constituent parts existed practically at the beginning of things, and also that it is not an element, but built up of two gases combined in a definite proportion, let us now take up the substance itself and study it in its various forms. These are quite numerous, but may all be classified under three fundamental heads: gaseous, liquid, and solid water.

The fact that it can exist in these three states is not so remarkable, since it is possible to transform every known substance, elementary or combined (provided the latter do not decompose) into these three states of aggregation; but that the three should all be within the range of ordinary temperatures is rather extraordinary. There are only a few common substances of which this is true, e. g., ammonia, benzene, etc. It will be seen, moreover, that water has a good many other noteworthy properties. As compared with other substances it is nearly always exceptional, and stands at the extremes.

Gaseous Water.—Steam and atmospheric water vapor belong in this category. It is not until we go to some of the arid desert regions of our earth that we realize the importance of the latter. Where there is no moisture in the atmosphere, there can be no clouds formed, and hence there can be no rain, which means, of course, that such a place must be