226 Prof, von Kobell upon Galvanography. 



application of a file. From the condition of the copper, it is 

 evident that its precipitation takes place in the form of an infini- 

 tude of extremely minute crystals, to the accumulation of which 

 the nodules and other asperities of the surface are to be ascribed. 

 As the deposit thus made has a tendency, especially at the first 

 stage of the progress, to spread out laterally, we observe, as has 

 already been remarked, that non-conducting surfaces also, when 

 interspersed at intervals with places that do conduct, and when 

 resting on good conductors, receive a similar coating of metal. 

 As soon as such non-conducting spots, however, begin to assume 

 the form of rounded masses, the lateral extension decreases very 

 materially and an increase takes place in the thickness of the 

 deposit. 



Now the quality of a galvanic plate depends upon the size, 

 or rather the uniform aggregation of these crystals, and this is 

 principally influenced by the strength of the galvanic current 

 and by the amount of resistance offered to its passage. Both 

 these circumstances are dependent on the dimensions of the pair 

 of plates and of the connecting strip ; on the distance between 

 the zinc and the other — the negative — plate ; on the nature and 

 on the concentration of the fluids employed, as also on their tem- 

 perature ; on the quality of the diaphragm interposed between 

 them ; and finally, on the nature and the surface of the colors 

 employed, supposing that a picture is to be coated and have a 

 copy taken from it. 



If a completely constructed and equable current were requisite 

 for obtaining a serviceable plate, these galvanic precipitations 

 would not, in all probability, come readily into practical use ; for 

 the strength of a current depends upon a great variety of circum- 

 stances, many of them extremely slight, as any one may convince 

 himself, by the employment of a galvanometer. Happily, how- 

 ever, it is constant enough for our purposes, namely, for the pro- 

 duction of a plate of sufficient coherence to resist the treatment 

 to which it is subjected by the copper-plate printer, and of suffi- 

 cient tenacity not to be liable to bend in passing between the 

 rollers ; and it is, moreover, a fortunate circumstance, that it is 

 matter of complete indifference whether the first film of copper 

 thrown down into the picture, and taking a perfect copy of it, is of 

 malleable and elastic metal, or brittle and fragile, provided the far- 

 ther thickness deposited thereon possesses the requisite properties. 



