230 Prof, von Kohell upon Galvanography. 



gether ; whereas the solution below the copper plate was of the 

 same blue color that it had at the beginning of the operation. 



Should the fluid not be renewed, the last portion of the cop- 

 per thrown down is not obtained in a sufficiently coherent 

 state, but there is deposited upon the plate a dark-brown volu- 

 minous slime. This precipitate consists chiefly of metallic cop- 

 per, and should the deposit not be too thick, it may be brought to 

 unite together, by renewing the precipitation fluid and employing 

 an energetic current. In such a case, however, it is advisable to 

 wash off" the slime with water, and, having dried the plate, to 

 give it a brilliant surface by the use of the scratch-brush, and 

 then replace it in the apparatus. 



(7.) The fluid for the zinc plate in the tamborine, or exciting 

 fluid. For this I employ water acidulated with sulphuric acid. 

 To a pound of water is added about j\ or -j-V of an ounce of En- 

 glish sulphuric acid. This mixture is to be poured over the zinc 

 plate, and the leaden plate placed thereupon, and it is well that 

 the fluid in the tamborine should stand somewhat above the level 

 of the precipitation fluid ; otherwise, undecomposed sulphate of 

 copper makes its way to the zinc, and the current is thereby re- 

 duced in energy. This exciting fluid is to be renewed every 

 day, and that which is saved may, if thought worth while, be 

 evaporated for the sulphate of zinc which it contains. 



Tn addition to this apparatus, the formation of these galvanic 

 plates requires a pair of pincers in order to remove the plates from 

 the fluid, inasmuch as it might prove injurious to wet the hands 

 too often with the copper solution. It is best to have copper pin- 

 cers. A few fine and coarse broad files are likewise wanted, as 

 are also a scratch-brush and other brushes, a vice, and a pair of 

 shears for cutting the plates. 



A representation of the apparatus, and a detailed description of 

 it, is given at the close of the paper. 



In using the apparatus, the following remarks must be attended 

 to. The tamborine is to be taken out of the fluid every twenty 

 four hours, and the zinc plate cleaned with water and a brush. 

 The parchment and the leaden plate are to be treated also in the 

 same way. This having been done, and the exciting fluid re- 

 newed, the zinc and the lead plates are to be replaced in the 

 apparatus. Should the lead plate become speedily coated with a 

 red film, or the upper surface of the zinc turn blackish, it is a 



