Electrolytic Determination of the Metals. 321 



is pressed over the stopper. The shaft is made in two parts as 

 a matter of convenience in removing the crucible and is joined, 

 with care to make a good contact between the two pieces of 

 shafting, by a rubber connector of sufficient thickness to pre- 

 vent the crucible from wabbling when rotated. 



The solution to be electrolyzed is placed in a beaker upon a 

 small adjustable stand, so that the crucible may be dipped into 

 the liquid to any desired depth. A platinum plate is employed 

 as an anode, and this is connected to the positive pole of a 

 series of four storage batteries, while the negative pole of this 

 series is connected to the bearing in which the shaft rotates, 

 thus allowing the current to go from the platinum plate 

 through the solution to the crucible, up the shaft of the motor 

 and back to the batteries. 



The power to run the motor is taken from the incandescent 

 light circuit of the street. 



The first attempts were made with the deposition of copper 

 from a solution of the sulphate, and the procedure was as 

 follows : The solution, 50 cm3 in volume, was placed in a 150 cm3 

 beaker and acidulated to give better conductivity. The stand 

 carrying the beaker was raised until the liquid covered about 

 two-thirds of the crucible adjusted to the shaft, thus giving a 

 cathode surface of about 30 cm2 . The anode was introduced and 

 the motor started. The wires from the storage batteries were 

 connected and the current allowed to pass through the solution. 

 The duration of the electrolysis was varied according to the 

 strength of current used, but in each case, after the deposit 

 was nearly complete, the current from the batteries was shut 

 oif, the motor stopped and the sides of the beaker, the platinum 

 anode, and the crucible were carefully washed with a fine jet 

 of water, the motor was again started and the current allowed 

 to pass for the remaining time. 



When the deposit was complete the crucible was removed 

 and washed, first with water, then with alcohol, and finally was 

 dried by passing it over a flame. 



Sulphuric acid [6 or 7 drops of the dilute acid— 1 : 4] was 

 generally used to acidulate the solution, since it was found 

 that the copper was deposited in a shorter time with sulphuric 

 than with nitric acid present. A few experiments were made 

 in which small amounts of nitric acid were used to show that 

 the copper could also be deposited completely in presence of 

 this acid. 



The following table show the results of a series of experi- 

 ments made as described above in solutions acidulated with 

 sulphuric acid. The standard of the solution of copper sul- 

 phate was fixed by the usual slow method of electrolytic 

 analysis. 



