412 



WELLS'S NATURAL PHILOSOPHY. 



How may wa 

 ter be decom' 

 posed ? 



Fig. 342. 



Thus, water is composed of two gases, oxygen and hydro- 

 gen united together. When the wires connecting the polea 

 of a galvanic battery are placed in water, and a sufEciently 

 strong current made to pass tlirough them, the water is decomposed, tho 

 hydrogen being given out at the negative pole of the 

 battery, and the oxygen at the positive pole. Fig. 

 342 represents a form of apparatus by which tliia 

 experiment can be performed in a very satisfactory 

 manner. It consists of two tubes, and H, sup- 

 ported vertically in a small reservoir of water, 

 and two slips of platinum, p p, which can be con- 

 nected with the poles of a voltaic battery, passing 

 in at the open end of tho tubes. When communi- 

 cation ia effected between the platinum slips and a 

 battery in action, gas rapidly rises in each tube and 

 collects in the upper part. In that tube which is in 

 connection with the positive polo of the battery oxygen accumulates, and in 

 tho other hydrogen. And it will bo noticed that the quantity of the latter ia 

 equal to twice the quantity of tho former gas, since water contains by volume 

 twice as much hydrogen as it does ox3'gen. 



The explanation of this phenomenon may be briefly given 

 as follows : — All atoms of matter are regarded as originally 

 charged with either positive or negative electricity. In tho 

 case of water, hydrogen is the electro-positive element and 

 oxygen the electro-negative clement. It has been already 

 shown that bodies in opposite electrical states are attracted by each other. 

 Hence, when the poles of a galvanic battery are immersed in water, the nega- 

 tive pole will attract the positive hydrogen, and the positive polo the negative 

 oxygen. If tho attractive force of the two electricities generated by tho bat- 

 tery is greater than the attractive force which unites the two elements, oxygen 

 and hydrogen, together in the water, the compound will be decomposed. Upon 

 tlio same principle other compound substances may be decomposed, by em- 

 ploying a greater or less amount of electricity. In this way Sir Humphrey 

 Davy made tho discovery that potash, soda, lime, and other bodies, were not 

 simple in their nature, as had previously been supposed, but compounds of a 

 metal with oxygen. ; 



782. Recent experiments have shown that the electricity 

 which dccomposL'S, and that which is evolved by tho decom* 

 position of a certain quan,tity of matter, are alike. Thus, wat^r i 

 is composed of oxygen and hydrogen ; now, if the electrical 

 power which holds a grain of water in combination, or which 

 causes a grain of oxygen and hydrogen to unite in tho right proportions 

 to form water, could be collected and thrown into a voltaic current, it 

 would be exactly the quantity required to produce tho decomposition 

 of a grain of water or the liberation of its elements, oxygen and hy- 

 drogen. 



What is tha 

 theory of the 

 decomposing 

 nction of gal- 

 vanic elec- 

 tricity ? 



Wliat quantity 

 of electricity is 

 necessary to 

 decompose a 

 •ubstance ? 



