Page:The fairy tales of science.djvu/95

 he came to be regarded as a great philosopher, though he still continued to earn his bread as a tutor. Such was the founder of the beautiful atomic theory of Chemistry, which is so well adapted to render certain natural laws intelligible to our understanding.

In examining the so-called four elements, we alluded to the fact that bodies united to form compounds in definite proportions. Let us explain this matter more fully. Water invariably contains oxygen and hydrogen, in the proportion of eight parts by weight of the former element to one part of the latter, whether these parts represent tons, pounds, grains, or any other quantities. The whole of the oxygen contained in the ocean is exactly eight times heavier than the hydrogen with which it is combined, and the weights of the two gases bear the same relation to each other in the dew-drop. If we take any other chemical compound, we shall find that the proportions by weight of its constituents are invariable; thus there is a broad distinction between such a compound and a mere mixture in which the ingredients are present in indefinite proportions.

Water is not the only compound that can be formed of oxygen and hydrogen. We can compel one part of hydrogen to combine with sixteen parts of oxygen, and the result of their union is a colourless liquid, less volatile than water, and having a metallic taste. This liquid, called peroxide of hydrogen, and water, are the only compounds that can be