304 Dr. Taylor and Mr. Inglis : 



is slowly dissolved by the sulphuric acid or by the aluminium 

 sulphate already in solution, and thus the film is continually 

 renewed on one side and dissolved on the other. If hydro- 

 chloric acid be used as electrolyte, the free chlorine acts on 

 the aluminium and forms a soluble salt A1C1 3 , and not a 

 difficultly soluble oxide. — This explanation is hardly sufficient, 

 for no reasons are given for the formation of secondary 

 oxygen ; and, further, aluminium sulphate is a fairly soluble 

 salt. Hence a full explanation is still wanting. 



Experimental Results. 



Experiments were made, in the first instance, to ascertain in 

 what way the addition of certain salts to the electrolyte affected 

 the aluminium anode. For this purpose the 12 volt storage- 

 battery of the laboratory was used, and in the circuit were a 

 3 ohm (approximate) resistance, an am meter which could be 

 read to O'Ol ampere and up to 3'0 amperes, and the electro- 

 lytic cell, all in series ; a voltmeter reading to 0'05 volt and 

 up to 15*0 volts was also in parallel circuit with the cell. 

 The cell consisted of a beaker containing a 1/1 molar solution 

 of sulphuric acid and the two electrodes, the one of sheet- 

 aluminium, and the other a spiral" of thick platinum wire. 

 The procedure was as follows : — The circuit was closed, with 

 the acid alone as electrolyte, and the readings of the volt- 

 meter and ammeter noted as soon as they became constant. 

 To the acid were added successive small quantities of a 

 solution of the salt under investigation ; and, after closing 

 the circuit, readings were noted every few minutes until they 

 again became constant. It was found necessary to use a 

 fresh piece of aluminium each time, as, through the continued 

 action of the weak current, the film on the anode became so 

 thick and resisting that addition of even large quantities of 

 potassium chloride had no influence on the current, although 

 a small quantity only was required when a fresh surface was 

 taken. It was therefore necessary to have the surface in as 

 uniform a condition as possible in order that the experiments 

 should be comparable, and this was most easily ensured by 

 using a fresh surface each time. 



Effect of Chloride and of Bromide. — The results are given 

 in the following tables. 



In the case of ammonium alum solution (Table I.) the effect 

 of potassium bromide was also determined, and after addition 

 of .0*3 c.c. of a I molar KBr solution, the current passed 

 freely, though it did not increase so rapidly as after addition 

 of chloride. 



