188 ELECTROLYSIS. 



Use the bath with laminated zinc electrodes. For plane- 

 surface pieces place a zinc sheet on each side : thus, for sheet 

 iron, place alternately one sheet of zinc and one of iron, and 

 so on. 



DEPOSITION OF IKON.* 



Iron has a very great chemical analogy with nickel, and the 

 majority of remarks made on nickeling apply to iron deposition. 

 The solutions are corresponding; iron taking the place of 

 nickel ; but, owing to the tendency of iron salts to acquire a 

 greater degree of oxidisation, the iron solutions become rapidly 

 altered. The hydrogen liberated by electrolysis goes to the 

 cathode, and the corresponding oxygen combines itself with 

 the iron anode, and has a tendency to produce basic salts. For 

 these reasons the double chloride of iron and ammonium is much 

 more advantageous than the sulphate. 



The double chloride of iron and ammonium is prepared by 

 dissolving unoxidised iron wire in hydrochloric acid, heating 

 at the end of the operation, and having an excess of iron to 

 prevent the formation of perchloride. For 60 grammes of 

 dissolved iron 55 grammes of ammonic chloride are added to 

 the solution. Mr. Sprague has found that the alteration of 

 the solution was retarded by the addition of a proportion of 

 glycerine. 



A solution of iron altered either by the action of the air or 

 by the generation of basic salts, can be renovated by adding to 

 it the suitable acid, heating the liquor until it is clear, and 

 sending through it an electric current for dissolving an iron anode. 



The iron deposition may be used for important scientific 

 experiments as regards the laws on magnetism, but it does not 

 seem to us to admit of lucrative industrial applications. Its 

 principal usefulness appears to consist in the steeling of electro- 

 types, which we have previously described. 



DEPOSITION OF TIN. 



Galvanic deposition of tin is not much in use, as tinning 

 by simple immersion or by contact with a second metal generally 



* Sprague, 1884 edition. 



