116 THE ROYAL SOCIETY OF CANADA 



It has been stated that the presence of zinc oxide in solutions 

 of zinc sulphate affected the deposit and so produced spongy zinc. I 

 have found the zinc uniformly good even with a considerable amount of 

 zinc oxide in the electrolyte. It is well known that zinc oxide and 

 sulphate unite to give a basic sulphate, but this compound is so inso- 

 luble that its presence in the solution can have little effect. 



Glue is frequently added during the electrolysis of certain solution 

 to improve the deposited metal, or to precipitate the colloids produced 

 in extracting the zinc from the calcined ore. Its influence on the 

 deposition of zinc is slight. The metal is a little smoother and some- 

 what brighter, while the current efficiency falls, apparently, two or 

 three per cent. 



Vigorous agitation with a stream of air has little influence on the 

 results of the electrolysis. The oxygen liberated at the anode, aided 

 in practise by the flow of the electrolyte through the cells, keeps a 

 sufficient amount of the zinc ions in the neighbourhood of the cathode. 



The effect of Free Acid. 



When an aqueous solution of zinc sulphate is electrolysed, zinc 

 and hydrogen are liberated at the cathode, and oxygen due to the 

 discharge of the SO4 ions, at the anode. Under the best conditions — 

 a high concentration of zinc and a low temperature — a certain amount 

 of hydrogen is liberated. As the temperature rises and the amount 

 of acid increases a large increase in the volume of hydrogen liberated 

 may be expected. 



In all conditions one gram equivalent of hydrogen and of metal 

 will be liberated by 96,500 coulombs, and by measuring the hydrogen 

 evolved, the efficiency of the process may be calculated. 



An apparatus, with a bell over the aluminium electrode, was 

 arranged so that the hydrogen could be measured at any time. The 

 current density was 28-30 amperes per square foot, and the efficiency 

 attained in the deposition of the zinc with varying zinc — acid ratios 

 can be seen from the curves. 



It will be noticed that a four per cent, zinc solution gives a higher 

 efficiency than a three per cent. Other experiments showed that a 

 six per cent, solution without free acid gave almost 100 per cent, 

 current yield. As might be expected, the efficiency of the process 

 fell off as the ratio of acid to zinc increased. 



The Effect of Different Current Densities on the Deposit. 



Aluminium electrodes of various sizes were placed in cells con- 

 taining filtered electrolyte and the current was passed between these 

 in series. The effect of high current density can be seen from the 



