formed of the two gases. This fact is well worthy of consideration. Hydrogen will combine with eight or with sixteen parts of oxygen, but in no other proportions. Let us now glance at some other compounds. The poisonous gas known as carbonic oxide, contains six parts of carbon and eight of oxygen; but six parts of carbon also combine with sixteen of oxygen to form carbonic acid. Again, in ordinary coal-gas we find one part by weight of hydrogen united to six of carbon.
How can we account for these recurrent numbers? What relation subsists between the number 8 or its multiple 16, and oxygen; between 1 and hydrogen; between 6 and carbon? Why should these three bodies combine in fixed numerical proportions?
According to the beautiful atomic theory of Dalton, these numbers express the relative weights of the ultimate particles of matter. Let us consider the composition of water in this light. The smallest possible particle of water is composed of one atom of hydrogen gas and one atom of oxygen, the latter being eight times heavier than the former. Now, it is evident that whatever may be the number of particles in a given volume of water, the relative weights of the two gases will remain constant. The smallest particle of the peroxide of hydrogen contains one atom of hydrogen and two atoms of oxygen; accordingly, there can be no compound of hydrogen and oxygen between water and the
