406 EECENT PROGRESS IN PHYSICS. 



In the heavy work of the Duke of Leuchtenberg the quantity of 

 gold precipitated was determined by chemical analysis. One decilitre 

 of the liquor was taken out of the gauged vessel before and after the 

 gilding, and examined ; very convenient methods of analysis were 

 contrived and an account of them published. — (Dingier' s Journal, 

 vol. 99, from Bulletin Scient. Figur. de St. Petersbourg.) It is evi- 

 dent that, in this case, only platinum anodes could be used. Small 

 objects were weighed before and after the gilding. Both methods are 

 unsuitable for the common gilder, and he can only judge of the strength 

 of the gilding by the commencement of a "matt" appearance on the 

 polished places. A compass inserted in the circuit would enable any 

 one, after a few trials, to determine approximately the quantity of 

 gold precipitated in a minute, even if it were not a tangent compass. 

 At any rate this would always reliably indicate the state of the current, 

 while the workman now has no means whatever of ascertaining when 

 it is growing weaker, and only knows by the evolution of gas and the 

 darkening of the color when it is too strong. 



Frankenstein introduced a new method of gilding, by which the 

 piece to be gilded is immersed in contact with zinc. The zinc is also 

 gilded or silvered, and the quantity of the precipitate is, according to 

 Fehling, (Dingler's Journal, vol. 78,) nearly proportional to the time. 

 The temperature is raised to 60° E., and the object must be taken out 

 and cleaned every ten or twenty minutes. Frankenstein recommends 

 for the gold solution six parts of prussiate of potash, four of carbonate 

 of potassa, ten of water, and one of chloride of gold; and for silver 

 five parts of prussiate of potash, five carbonate of potassa, two com- 

 mon salt, five aqua ammonia, and one chloride of silver. The liquid 

 should be boiled for a half to three-quarters of an hour and then de- 

 canted. This method has been frequently adopted by manufacturers ; 

 they use, however, the common solution of gold in cyanide of potas- 

 sium, adding a small quantity of caustic potassa or soda and wind 

 annealed brass wire loosel}'' around small objects, such as spoons, &c. 

 In this manner Frankenstein (Dingler's Journal, vol. 90) gilded the 

 cross and ball of a steeple in parts, and precipitated twenty-five ducats 

 upon a surface of fifty square feet, each piece being immersed three or 

 four times for five to ten minutes. The film of gold obtained by this 

 treatment was matt, which is always the case when as much as half a 

 ducat is precipitated upon a square foot. Such a gilding may, accord- 

 ing to the above mentioned experiments of Dumas, be considered equal 

 to a good fire gilding.* 



Becquerel (Dingler's Journal, vol. 92, Comptes Eendus, March, 

 1844, No. 2) has made numerous experiments on the precipitation of 

 metals from their solutions upon other metals, even upon zinc, in 

 which latter case he ascribed the precipitation to the galvanic currents 

 produced by the impurities in commercial zinc. He could only, as a 

 general rule, obtain adherent metallic deposits by contact with zinc, 

 and when the metallic salt to be precipitated was combined with an 

 alkali to form a double salt as nearly as possible neutral. In acid 



* By the use of brass wire with a piece of zinc at the end the gilding becomes reddish 

 in color, probably from the copper dissolved out from the brass. I have gilded iron in this 

 way without previous coppering. 



