CHEMICAL SCIENCE. 221 



ponent metals, copper and zinc, in the proportions in which they would form 

 brass, there will only be produced by the action of the battery a deposit of 

 real copper ; the zinc, more difficult of reduction, remains in solution. "What 

 must be done, then, to obtain a simultaneous precipitate of the two metals in 

 the proportions required, is either to retard the precipitation of the copper, or 

 accelerate that of the zinc. This may be done by forming the bath with a 

 great excess of zinc, and very little copper. Dr. Heeren gives the following 

 proportions as having perfectly succeeded: "There are to be taken of the 

 sulphate of copper 1 part ; warm water 4 parts ; and then sulphate of zinc 

 8 parts; warm water 16 parts; cyanide of potassium 18 parts; warm water 

 36 parts. 



Each salt is dissolved in its prescribed quantity of water, and the solutions 

 are then mixed ; and therefore a precipitate is thrown down, which is either 

 dissolved by agitation alone, or by the addition of a little cyanide of potas- 

 sium; indeed it does not much matter if the solution be a little troubled. 

 After the addition of 250 parts of distilled water, it is subjected to the action 

 of two Bunsen elements, charged with concentrated nitric acid, mixed with 

 one tenth of oil of vitriol. The bath is to be heated to ebullition, and is in- 

 troduced into a glass with a foot, in which the two electrodes are plunged. 

 The object to be covered is suspended from the positive pole. The two 

 metallic pieces may be placed very near. 



The deposit is rapidly formed if the bath be very hot ; after a few minutes 

 there is produced a layer of brass, the thickness of which augments rapidly. 

 Deposits of brass have been obtained in this way on copper, zinc, brass, and 

 Britannia metal ; these metals were previously well pickled. Iron may, prob- 

 ably, also be coated in this way ; but cast iron is but ill adapted for this 

 operation. London Mining Journal. 



NEW PKOCESS FOR ELECTEO-GILDLNTG. 



A new process for electro-gilding has been proposed by M. Briant, and 

 favorably reported on by the Academy of Sciences at St. Petersburg. It con- 

 sists essentially in the substitution of the oxyd for the chloride of gold in the 

 preparation of the gilding bath, and in the employment of a very feeble cur- 

 rent from a constant or sustaining battery. 802,88 grams of gold are to be 

 dissolved in nitric muriatic acid, and the solution evaporated, for the purpose 

 of obtaining the chloride of gold dry, and as free as possible from acid. The 

 chloride is then dissolved in 11 pounds of hot water, and 1,544 grains of well- 

 sifted magnesia added, and allowed to digest at a moderate temperature. The 

 oxyd of gold, when separated, is found in combination with the magnesia. 

 The magnesia, well washed, is then treated with water acidulated with nitric 

 acid, ha the proportion of 3,759 grains of acid to 5 kilograms of water. The 

 magnesia is dissolved by the acid, leaving the simple hydrated oxyd of gold, 

 which is now thrown upon a filter and washed till quite free of acid. 



It is with this oxyd of gold thus prepared that M. Briant proposes to form 

 his bath. He takes of yellow prussiate of potash 500 grains; of caustic pot- 

 ash 120 grains ; water 5 kilograms. To this solution the oxyd of gold with 



