116 GALVANIC ELECTRICITY. 



the evolution of gas immediately commences from the 

 the platinum wires. This compound battery will be 

 found rather slow in its operation, and has been de- 

 scribed only for the purpose of illustrating the use of 

 the more powerful galvanic batteries of similar con- 

 struction. The student is advised to substitute for it 

 the Voltaic pile, as hereafter described. 



278. AN EXPLOSIVE MIXTURE. A mix- 



What proper- , , 



ty has the ture of hydrogen and oxygen gases, in the 



US proportion m which they are here evolved, 

 is explosive. This property is the evi- 

 dence that the gases are really oxygen and hydrogen, 

 in due proportion. A sufficient quantity being col- 

 lected, the mouth of the tube is covered with the finger, 

 the tube inverted, and a match applied at the mouth. 

 A slight puff is all the evidence that will be obtained 

 from a small quantity of the mixture. A test-tube full 

 will give a sharp report. 



279. SEPARATE COLLECTION OF THE 



How may the , . , 



gate* be col- GASES. By using two test-tubes, instead 



lected*cpa- o f before described, and introduc- 



rately ? 



ing an electrode into each, the gases may 



be separately collected and tested by the methods give 

 in the section which treats of those gases. 



280. The water is acidulated in the ex- 



Wky is the . 



water to be de- penment, to make it a better conductor of 

 "dilated? the mmience which must pass through it, 

 from one electrode to the other, in order 

 that the decomposition may take place. The reason 

 for using platinum electrodes has already been given. 

 In the present case, if the copper wires themselves 



