of Electro-precipitated Metals- 17 



stances ; for instance, in the silver coating of a cylindrical 

 vessel having a flat bottom ; in it there will infallibly exist a 

 fissure at the angle formed by the cylinder and the bottom. 

 Hence we see the necessity of roundi7ig off' as much as pos- 

 sible all angles where we intend to deposit metals with the aid 

 of electricity. 



The surface of the mopld must consequently have an obvi- 

 ous effect on the deposit, inasmuch as no surface can be per- 

 fect in its polish ; hence it must necessarily follow that the 

 more gradual the undulations and depressions are, the more 

 cohesive will be the deposit ; a wax matrix is perhaps one of 

 the best substances to deposit on, and a polytype matrix, ob- 

 tained by pressing a woodcut into a melted metallic alloy when 

 near its point of solidification, one of the worst, for we have 

 on it a copy of all the pores of the wood ; besides, the alloy 

 being crystalline, its surface is, when microscopically exa- 

 mined, exceedingly rough. All abrupt deviations from the 

 original plane, though small, have an injurious effect on the 

 resulting deposit, and this increases with the depth ; but deep 

 or shallow, the result is the same, and differs only in amount. 



I have stated that all electro-metallic deposits are essentially 

 crystalline in their structure; this is readily proved by sub- 

 mitting them to the test of microscopic investigation, and 

 however carefully they be prepared, we shall perceive that 

 they consist of an assemblage of minute crystals more or less 

 perfectly formed. In Plate I. fig. 5 is represented a portion 

 of a beautiful deposit on a polished piece of metal after five mi- 

 nutes' action, the magnifying power employed being 300 times. 

 In it the crystalline structure is rendered apparent, and we see 

 moreover, here and there, groups of crystals starting up per- 

 pendicularly from the surface to a considerable height. Such 

 being the character of the first layers, the crystals, as in the 

 crystallization of a salt from its solution, increase in size, and 

 could we even obtain a perfect surface to commence on, we 

 must have, from the very nature of the process, the production 

 of inequalities, to which the shooting of these crystals above 

 the general surface mainly contributes ; these irregularities, as 

 before explained, can never perfectly be filled up, and a po- 

 rous structure must result ; add to this, that the crystallization 

 likewise spreads laterally from the summit of one group of 

 crystals to that of those in the neighbourhood, and it will be 

 readily perceived that spaces are here and there enclosed, 

 which can only become filled to the extent that the included 

 liquid is capable of yielding metal. Hence the microscope 

 reveals a structure such as I have delineated in fig. 2, which 

 is a section of electro-deposited copper magnified 100 times 



Phil, Mag. S. 3. Vol. 27. No. 177. My 1845. C 



