114 PRINCIPLES OF CHEMISTRY 



Water is a bad conductor of electricity that is, pure water does 

 not transmit a feeble current ; but if any salt or acid be dissolved in 

 it, then its conductivity increases, and on the passage of a current 

 through acidified water it is decomposed into its component parts. 

 Some sulphuric acid is generally added to the water. By immersing 

 platinum plates (electrodes) in this water (platinum is chosen because 

 it is not acted on by acids, whilst many other metals are chemically 

 acted on by acids), and connecting them with a galvanic battery, it 

 will be observed that bubbles of gas appear on these plates. The gas 

 which separates is called detonating gas? because, on approaching a 

 light, it very easily explodes. 3 What takes place is as follows : First, 

 the water, by the action of the current, is decomposed into two gases. 

 The mixture of these gases forms detonating gas. When detonating 

 gas is brought into contact with an incandescent substance for instance, 

 a lighted taper the gases re-combine, forming water, the combination 

 being accompanied by a great evolution of heat, and therefore the 

 vapour of the water formed expands considerably, which it does very 

 rapidly, and as a consequence of which an explosion takes place -that 

 is, sound and increase of pressure, and atmospheric commotion, as in 

 the explosion of gunpowder. 



In order to discover what gases are obtained by the decom- 

 position of water, the gases which separate at each electrode must 

 be collected separately. For this purpose a V-shaped tube is taken ; 

 one of its ends is open, and the other fused up. A platinum wire, 

 terminating inside the tube in a plate, is fused into the closed end ; 



He was only convinced of the fact that water contains nothing but hydrogen and oxygen 

 by a long series of researches, which showed him that the appearance of an acid and 

 alkali in the decomposition of water proceeds from the presence of impurities (especially 

 from the presence of ammonium nitrate) in water. A final understanding of the com- 

 position of water is obtained from the determination of the quantities of the component 

 parts which enter into its composition. It will be seen from this how many data are 

 necessary for proving the composition of water thai is, of the transformations of 

 which it is capable. What has been said of water refers to all other compounds ; the 

 investigation of each one, the entire proof of its composition, can only be obtained by the 

 juxtaposition of a large mass of data referring to it. 



2 This gas is collected in a voltameter. 



3 In order to observe this explosion without the slighest danger, it is best to proceed 

 in the following manner. Some soapy water is prepared, so that it easily forms soap 

 bubbles, and it is poured into an iron trough. In this water, the end of a gas-conducting 

 tube is immersed. This tube is connected with any suitable apparatus, in which 

 detonating gas is evolved. Soap bubbles, full of this gas, are then formed. If the 

 apparatus in which the gas is produced be then removed (otherwise the explosion might 

 travel into the interior of this apparatus), and a lighted taper be brought to the soap 

 bubbles, a very sharp explosion takes place. The bubbles should be small to avoid any 

 danger ; ten, each about the size of a pea, suffice to give a sharp report, like a pistol 

 shot. 





