Royal Society. 147 



In silvering, the plates are placed in pairs vertically in the 

 trough, the silvering -solution A is mixed with water in a sepa- 

 rate vessel, the reducing-liquid mixed, and the trough filled ; in 

 winter it is convenient to use warm water, so that the tempera- 

 ture may be from 20° to 28°. 



Glasses for optical purposes must be silvered in a horizontal 

 position, so as to touch the surface of the liquid; the silver 

 surface must be transparent with a blue colour ; it must be bril- 

 liant, and must adhere so firmly that it is not rubbed off when 

 polished. 



This mode of silvering is calculated for the manufacture of 

 mirrors the cost of preparing which shall not exceed that of 

 the commonest sorts. Special determinations show that' with 

 these mixtures perfect mirrors can be prepared with a quan- 

 tity of silver not exceeding 3 to o\ grammes in a square metre. 



Without the addition of copper this cannot be effected ; I am 

 not in a position to give an explanation of this. The action of 

 copper is at once recognized, if a very dilute solution free from 

 copper be mixed with solution of sugar and allowed to stand ; 

 the deposit of silver is then full of white spots and of holes ; if 

 a trace of copper be present, the deposit is lustrous and free 

 from faults ; and with more copper no silver is deposited. In 

 this case there are actions of adhesion at work quite out of the 

 range of theoretical considerations. The point is to give the 

 particles of the liquid less adhesion to the silver than is possessed 

 by the particles of the glass whose surface is moistened by the 

 liquid ; when the adhesion of the particles is greater, the glass 

 is not coated. 



The silvering in a large looking-glass manufactory near 

 Nuremberg has been effected by the above, process for more 

 than a year, and produced very beautiful articles, which, how- 

 ever, met with no sale. It is to be expected that in the course of 

 time the prejudices against silver looking-glasses will disappear. 



XVII. Proceedings of Learned Societies. 



ROYAL SOCIETY. 

 [Continued from vol. xxxiv. p. 545.] 

 Dec. 5, 186/.— Dr. W. A. Miller, Treas. and V.P., in the Chair. 

 rrVHE following communication was read : — 



H " On some Alterations in the Composition of Carbonate-of-Lime 

 Waters, depending on the influence of Vegetation, Animal Life, 

 and Season." By Robert Warington, F.R.S., F.C.S. 



In carrying out through a series of years the principles of the 

 aquarium for sustaining animal life in a confined and limited por- 

 tion of water through the medium of growing vegetation *, I had 

 observed that, during the summer months of the year, a consider- 



'L2 



