180 ELECTROLYSIS. 



the lines might come thick, which should be particularly 

 avoided. 



Before beginning the deposition of iron, it is necessary to 

 perfectly clean the electro and rub it after with caustic potash. 



FIG. 31. 



Finishing Machine for Electros. 



The bath is principally composed of ammonic carbonate in 

 the proportion of 12 kilogrammes of carbonate to 75 litres of 

 water. The iron must be dissolved in the solution by immersing 

 an anode of charcoal iron connected with the positive pole of a 

 3 or 4 Bunsen cell battery. A second iron plate is connected 

 to the negative pole, and the deposition is from time to time 

 tested by replacing the cathode by a copper plate. 



With one or the other of these baths, the operation is con- 

 ducted as follows : 



An anode of the best quality of charcoal iron is used, and a 

 current of about 4 volts is sent through the bath. The deposi- 

 tion is not immediate as is the case with copper: the electro 

 to be steel coated must remain immersed during a few minutes ; 

 after four or five immersions the deposit will be of a sufficient 

 thickness. 



The plates thus coated must, as soon as taken out of the 



