MECHANICS AND USEFUL ARTS. 89 



" A continuation of the experiments for several days produced 

 no better results, the sohition not improving by use, as is often the 

 case with copper solutions used in electrot3^ping. An employ- 

 ment of a weaker battery improved the results, but still left much 

 to be desired. An examination of the bath showed an increasing 

 acid reaction, owing to the deposition of iron upon the cathode 

 more rapidly than it was dissolved from the anode. To augment 

 the solubility of the anode, a plate of copper was plunged in the 

 bath and combined with the iron. 



" The result of this combination was most surprising; not only 

 did the baths in the first category become re-neutralized in a few 

 hours, but the deposits became much smoother, their color a dull 

 gray, and adhered perfectly to the cathode without forming bub- 

 bles or cracking in any part. Their surfaces remained quite 

 smooth during the first 24 hours, after which there began to form, 

 in several places, the characteristic cavities, corresponding, so 

 to speak, with those mammillary bubbles so olten seen in the 

 electro-deposition of copper. By reducing the energy of the cur- 

 rent, either by reducing the strength of the solution or increasing 

 the resistance in the solid parts of the circuit, so as to render the 

 evolution of gas imperceptible, the formation of these bubbles 

 ceased entirely. M. Klein found the strength of the solution 

 should vary with the material of which the cathode was made. In 

 all cases the cathode was required to be perfectly clean and 

 smooth. 



*' Galvanic iron, when first taken out of the bath, is as hard as 

 cast steel, and very brittle, but when annealed at a temperature 

 of dull redness it loses much of its harshness and hardness : when 

 further annealed to red heat it is malleable, and may be engraved 

 as easily as soft steel. 



" When made under favorable conditions, and annealed uni- 

 formly, and with the proper precautions, electro-deposits are not 

 subject to twist, bend, or blister. There is no contraction, but, on 

 the contrary, an almost imperceptible dilatation. This is of im- 

 portance where the complete similarity of blocks is required, as 

 tneir dimensions should receive no sensible alteration on being 

 annealed. The specific gravity of this iron before and after an- 

 nealing has not been yet determined. 



"It appears that galvanic iron has no permanent magnetism, 

 but will receive magnetism like soft steel." 



THE COLORING OF BRASS. 



Some interesting details have lately been published respecting 

 this very practical subject in a German cotemporary, illustrating 

 the methods emplo3'ed in obtaining a color of any required tint. 

 An orange tint, inclining to gold, is produced by first polishing the 

 brass and then plunging it for a few seconds into a neutral solution 

 of crystallized acetate of copper, care being taken that the solution is 

 completely destitute of all free acid and possesses a warm temper- 

 ature. Dipped into a bath of copper, the resulting tint is a griiy- 



8* 



