THE ro.MI'OSlTlnN OF WATEU, HYDROGEN' 118 



Lavoisier, Fourcroy, and Vauquelin. They obtained four ounces of 

 water by burning hydrogen, and found that water consists of 15 parts 

 of hydrogen and 85 parts of oxygen. It was also proved that the 

 weight of water formed was equal to the sum of the weights of the 

 component parts entering into its composition ; consequently, water con- 

 tains all the matter entering into oxygen and hydrogen. The com- 

 plexity of water was proved in this manner by a method of synthesis. 

 But we will turn to its analysis i.e., to its decomposition into its com- 

 ponent parts. The analysis may be more or less complete. Either 

 both component parts may be obtained in a separate state, or else 

 only one is separated and the other is converted into a new compound 

 in which its amount may be determined by weighing. This will be a 

 reaction of substitution, such as is often taken advantage of for 

 analysis. The first analysis of water was thus conducted in 1784 by 

 Lavoisier and Meusnier. The apparatus they arranged consisted of a 

 glass retort containing water, naturally purified, and whose weight had 

 been previously determined. The neck of the retort was inserted into 

 a porcelain tube, placed inside an oven, and heated to a red heat by 

 charcoal. Iron filings, which decompose water at a red heat, were 

 placed inside this tube. The end of the tube was connected with a 

 worm, for condensing any water which might pass through the tube 

 unclecomposed. This condensed water was collected in a separate flask. 

 The gas formed by the decomposition was collected over a water bath 

 in a bell jar. The aqueous vapour in passing over the red-hot iron was 

 decomposed, and a gas was formed from it whose weight could be 

 determined from its volume, its density being known. Besides the 

 water which passed through the tube unaltered, a certain quantity of 

 water disappeared in the experiment, and this quantity, in the experi- 

 ments of Lavoisier and Meusnier, was equal to the weight of the gas 

 which was collected in the bell jar plus the increase in weight of the 

 iron filings. Hence the water was decomposed into a gas, which was 

 collected in the bell jar, and a substance, which combined with the 

 iron ; consequently, it is composed of these two component parts. This 

 was the first analysis of water ever made ; but here only one (and not 

 both) of the gaseous component parts of water was collected separately. 

 Both the component parts of water can, however, be simultaneously 

 obtained in a free state. For this purpose the decomposition is brought 

 about by a galvanic current or by heat, as we shall learn directly. 1 



1 The first experiments of the synthesis and decomposition of water did not afford, 

 however, an entirely convincing proof that water was composed of hydrogen and oxygen 

 only. Davy, who investigated the decomposition of water by the galvanic current, 

 thought for a long time that, besides the gases, an acid and alkali were also obtained. 



VOL. I. I 



