124 ELEMENTS OF LABORATORY WORK 



solutions to the same conditions for any length of time. The 

 plates are then detached, dried, and weighed. It will be 

 found : 



1. That one of the plates in each solution has increased 

 in mass, while the other has decreased to the same extent. 

 The one which increases has always the same relative position 

 in the circuit. 



2. That the quantity of copper so acted upon is the same 

 in the solutions of copper sulphate and copper nitrate. 



3. That the quantity of silver affected differs from that of 

 copper, and bears to it the ratio of 108 to 31*5. A repetition 

 of the experiment will show that the relation between the 

 quantities of silver and copper is maintained. By including 

 other solutions in the circuit, the relative quantities of other 

 substances liberated may be obtained. 



The gain in the mass of one plate, coinciding with an 

 equivalent loss from the other, would indicate that there is a 

 transference of material from one plate to the other. By sub- 

 stituting platinum plates, however, it may be shown that this 

 is not so ; for then an increase alone takes place, the other- 

 plate not diminishing in mass. It is probable, therefore, that 

 the loss of material from one of the plates is a secondary 

 change, due to the solvent action of the altered liquid upon it. 

 It becomes a matter of further investigation why the quan- 

 tities should in this case be equal. The explanation will be 

 found to lie in the mutual relations of the constituents of the 

 substance decomposed. 



It may be noticed here that the electric circuit gives an 

 opportunity of submitting several bodies simultaneously to 

 exactly the same conditions relatively to electric stress. 

 Whatever variation there may be in various portions of the 

 circuit, and however varied may be the changes going on, 

 there is the same electric stress throughout. 



82, Decomposition of a Body by Close Contact with 

 another Body, Formation of new kinds of Matter when 

 Two Bodies react Chemically. A piece of zinc is added to 

 some dilute hydrogen sulphate. It dissolves, while bubbles of 

 gas come off, and the temperature of the liquid rises. If the 



