re 



REPORT 1873. 



if it he brought into contact with another metal still further removed from the 

 power of effecting the decomiDosition of water, the electric force started by the con- 

 tact of the two metals enhances the chemical affinity sufficiently to make it effec- 

 tive ; or (otherwise expressed) the joint tension upsets the state of equilibrium 

 between the oxygen and hydrogen. The junction of the metals may be made 

 outside the water by a wire, and the amount of action may be determined by a 

 Thomson's galvanometer. The effect of varying the distance of two plates of zinc 

 and copper was tried ; and it was found that the chemical action increases slowly till 

 the plates are within about an inch of one another, but on continuing to bring them 

 nearer the action increases at a rapidly accelerating ratio. If the water be heated 

 when it is exposed to this joint action of chemical and electrical force, it decom- 

 poses more readily. In experiments made with two plates about 1-5 inch distant 

 from one another, the deflection of the galvanometer showed that the effect of 

 raising the temperature from 40° C. to 80° 0. was more than double of that between 

 20" C. and 40° C. ; but in an experiment made where the copper was deposited in 

 a spongy condition on the zinc, and the hydrogen gas produced was collected, the 

 following numbers were obtained :^ 



The last column shows the extraordinary acceleration of the action due to heat. 



Magnesium is capable by itself of decomposing water ; but its action is greatly 

 increased by touching it with a piece of copper, and some of the hydrogen gas then 

 makes its appearance on the copper plate. 



If instead of magnesium we take a metal less capable than zinc of decomposing 

 w.ater, we still find a deflection of the galvanomet.'r if it be united with another 

 metal still more " negative." The order for pure water seems to be : — platinum, 

 silver, copper, iron, tin, lead, zinc, magnesium. 



Experiments were made on the effect of electrical action by using the force 

 generated in one cell of Daniell, instead of the force generated by the contact of 

 the metals experimented on. It might be inferred that the electrolysis of water 

 would be more easily effected between poles made of a metal that has a consi- 

 derable affinity for oxygen than between polos of a metal which has little affinity. 

 And so it is. "NA'^hen zinc poles were used, there was found to be more than double 

 the action that there was wlien platiiuim poles of the same size and at the same 

 distance were employed. The order of efficiency for poles in the electrolysis of 

 water seems to be : — platinum, tin, silver, copper, iron, lead, zinc, magnesium. 

 After a few minutes the power of tin was found to rise above that of copper. The 

 other metals are in the same order as in the previous list, where they themselves 

 produced the electricity by their joint action on water. 



The effect of heat on the electrolysis of water was tried with two zinc poles. 

 The deflection increased .about fourfold between 5° C. and 80° C, and the action 

 increases nearly 2}(iii ^Htssn with the temperature. 



If instead of employing two poles of the same metal we use dissimilar metals, 

 ■w-e have a current established by these two metals which, according to its direction, 

 either adds to or subtracts from the current originating in the Daniell's cell. 

 Thus if two poles of platinum bo employed the effect with water is very minute ; 

 but if the negative pole be replaced by one of zinc, pure water is decomposed by 

 one cell of D.aniell's battery with visible evolution of hydrogen gas, The experi- 

 ment was performed quantitatively with poles of silver and zinc. 



