no PHYSIOGRAPHY. [chap. 



action of chemical agencies, on one or other of its com- 

 ponents, is now complete. On the one hand, it has been 

 seen that certain metals remove the oxygen and set free 

 the hydrogen ; on the other hand, chlorine removes the 

 hydrogen and sets free the oxygen. Had these experi- 

 ments been conducted with great care, the balance being 

 used at each step, it would have been possible to determine 

 the precise proportions in which oxygen and hydrogen exist 

 in water. In fact, the experiment with iron furnished the 

 French chemist, Lavoisier, with the means of proving the 

 composition of water analytically for the first time. Suppose 

 a given v/eight of water in the form of steam be passed 

 through the hot-iron tube, and that the oxide of iron which 

 is produced be weighed to ascertain how much oxygen 

 has been obtained ; it is thus easy to tell how much oxygen 

 exists in a given weight of water, and the rest will of 

 course be hydrogen. In this way it has been found that 

 loo parts by weight of water contain SS'Sg of oxygen and 

 I I'll of hydrogen; in other words f by weight of water 

 consists of oxygen, and ^ of hydrogen, so that every 9 

 pounds of water contain 8 pounds of oxygen and i of 

 hydrogen. This, therefore, is the composition of water 

 by weight, and it agrees perfectly with what was deduced 

 from our first electrical experiment with reference to the 

 composition of water by volume. It was then found, in 

 dealing with bulks, that twice as much hydrogen as oxygen 

 was obtained from water. Now oxygen is sixteen times 

 heavier than hydrogen, taking bulk for bulk ; if therefore 

 we obtained from a given quantity of water a volume of 

 oxygen that weighed 16 grains, then we should find an equal 

 volume of hydrogen weighed i grain ; but, as a matter of 

 fact, we obtained in our experiment twice the bulk of hydro- 

 gen, so that this quantity, instead of weighing i grain, must 



