1856.] and on Divided Gold. 809 



added to the remaining solid matter, that as much may be dissolved 

 as possible ; and the clear fluids to be put together and increased by 

 the further addition of 61 cubic inches of water. This is the silver- 

 ing solution, No. 1 ; a second fluid. No. 2, is to be prepared in like 

 manner, with this difference, that the tartaric acid is to be doubled 

 in quantity. The apparatus employed for the silvering of glass 

 plate consists of a cast-iron table box, containing water within, and 

 a set of gas-burners beneath to heat it : the upper surface of the 

 table is planed and set truly horizontal by a level, and covered by 

 a varnished cloth : heat is applied until the temperature is HO^Fah. 

 The glass is well cleaned, first with a cloth ; after which a plug of 

 cotton, dipped in the silvering fluid and a little polishing powder, 

 is carefully passed over the surface to be silvered, and when this 

 application is dry it is removed by another plug of cotton, and 

 the plate obtained perfectly clean. The glass is then laid on the 

 table, a portion of the silvering fluid poured on to the surface, and 

 this spread carefully over every part by a cylinder of india-rubber 

 stretched upon wood which has previously been cleaned and wetted 

 with the solution ; in this manner a perfect wetting of the surface 

 is obtained, and all air bubbles, &c. are removed. Then more 

 fluid is poured on to the glass until it is covered with a layer 

 about the j^^th of an inch in depth, which easily stands upon it ; 

 and in that state its temperature is allowed to rise. In about 10 

 minutes or more silver begins to deposit on the glass, and in 15 or 

 20 minutes a uniform opaque coat, having a greyish tint on the 

 upper surface, is deposited. After a certain time the glass em- 

 ployed in the illustration was pushed to the edge of the table, was 

 tilted that the fluid might be poured off", was washed with water, 

 and then was examined. The under surface presented a perfectly 

 brilliant metallic plate of high reflective power, as high as any that 

 silver can attain to ; and the coat of silver, though thin, was so 

 strong as to sustain handling, and so firm as to bear polishing on 

 the back to any degree, by rubbing with the hand and polishing 

 powder. The usual course in practice, however, is, when the first 

 stratum of fluid is exhausted, to remove it, and apply a layer of 

 No. 2 solution ; and when that has been removed and the glass 

 washed and dried, to cover the back surface with a protective coat 

 of black varnish. When the form of the glass varies, simple 

 expedients are employed ; and by their means either concave or 

 convex, or corrugated surfaces are silvered, and bottles and vases 

 are coated internally. It is easy to mend an injury in the silvering 

 of a plate, and two or three cases of repair were performed on the 

 table. 



The proposed advantages of the process are, — the production 

 of a perfect reflecting surface ; the ability to repair ; the mercantile 

 economy of the process (the silver in a square yard of surface 

 is worth \s. Sd.) ; the certainty, simplicity, and quickness of the 

 operation ; and, above all, the dismissal of the use of mercury. In 



