TRANSACTIONS OF THE SECTIONS. 



71 



the cell -witli the copper plate, the specific gi-avity of the liquid having risen from 

 1-015 to 1-047. 



A similar experiment was tried with plates of copper and zinc in sulphate of 

 copper and sulphate of zinc respectively. The result was as before, metaUic copper 

 being deposited on the copper plate, and the sulphate of zinc rising in specific 

 gravity from l-12:j to 1-189. 



In order to determine whether the amount of silver deposited depended, not 

 merely on the amoimt of the silver in solution, but also on the amount of copper 

 salt that bridged over the intervening space, similar experiments were made in 

 which the nitrate of silver was kept constant, but the nitrate of copper was increased 

 by equivalent multiples. It was foimd that the silver deposited increased -with the 

 increase of the cojjper salt, being about double when the copper salt was seven 

 times as strong, and that the effect of successive additions gi-adually diminished. 

 This is in strict accordance with other experiments, showing that, when the copper 

 plate is immersed in a mixture of the nitrates of copper and silver, the amount of 

 silver deposited is iucreased, and increases with each successive addition of copper 

 salt, though in a diminishing ratio. 



That this acceleration is not produced by a copper salt only was proved by re- 

 peating the experiment with a variety of other nitrates. 



The subjoined Table shows the results, and indicates, at the same time, that the 

 increased effect does not depend simply upon the nitric element, which was present 

 in the same quantity in all, but likewise on the nature of the salt. 



Size of plate 32.30 sq. miUims. ; vohune of solution 72 cub. centi 

 2-8 per cent, of nitrate of silver ; temperature 18° C 



time 5 mmutes. 



centims., containing 



On Crystals of Silver. By J. H. Gladstone, F.R.S. 



The crystalline deposit on copper or zinc immersed in silver nitrate forms a 

 very beautiful object when viewed under the microscope. The form, colour, and 

 general character of it depend vei-y much on the strength of the solution ; if weak, 

 say 1 per cent., the red metal is presently covered with a growth of small crystals, 

 which are quite black ; but as the action proceeds some of these crj'stals grow 

 ■more rapidly than others, especially at the angles of the plate, and the new growth 

 is white. If the solution be stronger, say 3 per cent., there is no black deposit, 

 but the white silver simulates the appearance of furze-bushes or fern-leaves of 

 varied structure. In much stronger solutions, say 12 per cent., the crystals re- 

 minded the author of juniper-branches, and in stronger still they had rather the 

 outward form of moss. In nearly saturated solutions the crystals of silver end in 

 thick knobs. The crystals at first advance pretty uniformly into the liquid, but 

 when they have considerably reduced its strength, there usually happens a stop- 

 page of the general advance, and a special growth from one or two points, forming 

 long feathery crystals, that sweep rapidly through the lower part of the solution. In 

 a 1 per cent, solution these are long meandering threads, with tufts like the den- 

 dritic appearances in minerals. The crystals are peculiarly beautiful when nitrate 



