xvi WATER AND THE ELEMENTS COMPOSING IT 241 



Such a process as this, the formation of a compound from 

 elements, or from simpler materials, is known as a synthesis. 



We might also find the required ratio by the analysis of 

 water, that is by breaking it up into its components,-which we can 

 do by passing an electric current through it. 



EXPT. 247. This may be done by means of an electric 

 battery for generating the electric current and a Voltameter. 

 The latter is most simply made by closing the bottom of a 

 funnel by means of a tightly fitting cork through which pass 

 two platinum wires with small plates of platinum attached to 

 the ends remaining in the funnel (Fig. 125). Over these 



FIG. 125. A Voltameter. 



plates are supported two glass test-tubes, and the tubes and 

 part of the funnel are filled with water to which has been 

 added a little sulphuric acid, as otherwise it offers great resist- 

 ance to the electric current. The wires from a battery of three 

 or four cells are connected with the ends of the platinum wires, 

 and as soon as the connection with the battery is complete, 

 provided there is clean metal at every junction, bubbles of gas 

 are seen to rise from each platinum plate and to ascend into 

 the tube and displace the contained liquid. After the 

 experiment has gone on for half-an-hour, the gases may 



B 



