394 Mr. T. Gray on the Electrolysis 



out by Lord Rayleigh, to make the deposit less adherent and 

 more roughly crystalline. There is then a tendency for the 

 deposit to grow out from the cathode towards the anode in 

 long branch-like crystals. This tendency is increased by 

 any sharp corner on the cathode-plates, and hence care 

 must be taken to round the corners and smooth the edges 

 thoroughly. The deposit also deteriorates as time goes on in 

 consequence of the crystals presenting sharp protuberances, 

 which tend to grow and become more and more prominent. 

 It follows that a somewhat smaller plate or greater density of 

 current can be used if the time be short; but I have generally 

 found that when the density of the current is such that the 

 deposit would deteriorate greatly during the first two or three 

 hours, the adhesion to the plate is likely to be uncertain. 

 The best results seem to be obtained with a solution contain- 

 ing about five per cent, by weight of nitrate of silver, and 

 cathode-plates which present an area of not less than 200 nor 

 more than 600 square centimetres per ampere of current. If 

 this strength of solution and size of plate be used and the 

 plates be properly cleaned, the deposit is very compact and 

 finely crystalline, and adheres very firmly to the surface of 

 the plate. When the strength of the solution is increased the 

 size of the plate can be slightly diminished, but not by any 

 means in the proportion of the increased quantity of silver in 

 the solution ; the deposit is then more roughly crystalline, will 

 not bear lengthened application of the current, and adheres 

 much less firmly to the plate. So far as these experiments 

 have gone, it seems a mistake to use a solution containing 

 more than, or even as much as, ten per cent, of silver nitrate. 

 Solutions containing from three to thirty per cent, have been 

 repeatedly tried; but the best results have always been obtained 

 with solutions containing from four to ten per cent. There 

 seems no reason for using strong solutions except a slight 

 difference in the original cost of the plates; but as these may 

 be of very thin metal, the cost is a small matter compared 

 with the risk of either total or partial failure of the experiment. 

 When the loss or anode-plates are to be used simply to 

 supply silver to the solution, they need not be larger than the 

 gain or cathode-plates; and there is some advantage in making 

 them smaller, so as to increase the distance of the edges of the 

 cathodes from those of the anodes. When the plates are 

 small the surface becomes very soft and spongy, and if the 

 density of the current exceed a certain moderate amount they 

 will blacken, and the resistance of the cell is apt to become 

 variable, due to the liberation of gases. It is better to make 

 the anodes a good deal larger than the cathodes, because in 



