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4th December^ l8g4. 



Mr. J. Brown read a Paper on 

 ELECTROLYTIC CRYSTALLIZATION OF METALS. 



The metals are electrolytically deposited from aqueous solutions 

 of their compounds, contained in little cells* provided with 

 platinum wires for connexion to the battery. The cells are of 

 a form suitable for the lantern microscope by which images of 

 the crystals in the act of formation are projected on the screen. 

 The electrolytic crystallization of metals has been studied by Dr. 

 Gladstone and others, but I am not aware that the actual 

 growing of the crystals has ever before been exhibited to an 

 audience. The effect on the screen is very striking and in some 

 cases the forms observed are very curious and beautiful. 



The solutions to be operated upon contain stannous chloride, 

 lead acetate, silver nitrate, cupric chloride and cadmium chloride; 

 the last mentioned repeated with litmus coloration to show the 

 evolution of chlorine as hydrochloric acid at the positive pole. 

 The effect of this evolution of chlorine or other anion is also 

 seen when, after the formation of a deposit of metallic crystals 

 on one pole, the current is reversed and the chlorine attacks the 

 metal previously deposited and dissolves it off in combining 

 with it to re-form the chloride. 



The accompanying figures from photo-micrographs illustrate 

 two of the forms observed. In both cases TVdenotes the position 

 of the negative pole from which the crystals grow. The crystal 

 of tin, fig I , forms very rapidly in a concentrated solution of the 

 chloride under the influence of a battery of about three volts 

 electromotive force. The rapid shooting out across the screen 

 of the image of such a crystal or congeries of crystals is very 



* I am indebted to the kindness of Mr. W. S. M'Kee for the construction of a 

 number of these cells. 



