RECENT PROGRESS IN PHYSICS. 401 



a lon<if continued operation, the odor of prussic acid proved injurious,* 

 and the prussiate of potash frequently produced a hluish green sedi- 

 ment, (Eisner, Dingler's Journal, vol. 88,) while the cyanide of 

 potassium was too expensive, before Liebig had made known his new 

 method of preparing it. At first, also, the gilding was not made 

 heavy enough, singular notions of saving gold being then prevalent, 

 and in tliis way the process fell into disrepute witli the public, and, 

 in fact, fire gilding can never be made so poor as that done by means 

 of galvanism. At first, too, especial importance was attributed to 

 the fact that the articles could be entirely finished before exposing 

 them to the process of gilding, and only after some experience it was 

 ascertained that heavy gilding was always without polish (matt;) 

 that by the use of varnish or wax certain places could be protected 

 against the deposit of gold was immediately observed by Ruolz, and 

 it was also soon known that a reddish hue might be given to the 

 gilding by the addition of cyanide of copper. — (Eisner, Dingler's 

 Journal, vol. 88.) 



At the present time the cyanide of potassium usually employed is 

 that prepared after Liebig's method, as any one can make it for him- 

 self, although it is still rather expensive, as the product is small for 

 tire quantity of material employed. The following is Liebig's direc- 

 tion, (Dingler's Journal, vol. 84, from the Annalen der Chemie und 

 Pharmacie, Marz, 1842 :) Eight parts of prussiate of potash are to be 

 thoroughly dried by gentle calcination upon a hot iron plate ; then 

 powdered and intimately mixed with three parts of dry carbonate of 

 potassa ; put at once into a Hessian crucible previously raised to a 

 dull red heat, and which has to be kept at this temperature ; the 

 mixture melts to a brown magma, with a lively evolution of gas ; 

 after some minutes, when the fluid mass becomes red hot, the color 

 grows lighter, and after prolonged fusion the contents of the crucible 

 appear limpid and amber yellow. If, from time to time, a hot glass 

 rod is immersed and then withdrawn, the adhering substance, when, 

 cooled, at first is brown, after a while it is yellow, and at last, when 

 the operation is finished, the drop on the glass rod is limpid and 

 colorless like water, and congeals to a perfectly white crystalline mass. 



During the fusion brownish flakes are seen floating about in the 

 fluid, which unite at last into a sponge-like mass, and assume a light 

 gray color. If the crucible is then taken from the fire and somewhat 

 cooled, in most cases the whole of this gray powder settles at the bot- 

 tom ; by stirring once or twice with the glass rod this deposition is 

 facilitated. The supernatant fused mass can now easily be poured 

 out into a heated porcelain dish, so that, with a little care, not a par- 

 ticle of the sediment passes over. 



This mass is then broken to pieces and preserved in well-closed 

 vessels, as it readily deliquesces and decomposes when liquified. 



The solution of gold is j^i'epared in the following manner : The 

 gold is rolled thin, cut up, and then heated in a porcelain dish, on 

 a water bath with seven times its weight of muriatic acid, to which 



•~" In tliis case ventilation is tlie only applicable remedy ; but, in iuldition, the cyanogen 

 compounds produce all the symptoms of poisoning with prussic acid when brought into 

 contact with sore hands, &c., and the greatest precaution is certainly advisable. 



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