222 ANNUAL OF SCIENTIFIC DISCOVERY. 



the filter is added, and the whole boiled for twenty minutes. The oxyd of 

 gold dissolves, and there is formed at the same time a precipitate of sesqui- 

 oxyd of iron. It is allowed to cool, and is then filtered, by which a yellow 

 liquid fit for use is obtained. The objects to be gilded should be well cleaned, 

 and attached to the negative pole of an element of Darnell's battery, while a 

 plate of platinum is attached to the positive pole. The gilding maybe effected 

 either in a warm or cold solution ; in the first case a deposit forms more rap- 

 idly, but with less delicacy. In order to obtain a durable deposit, analogous 

 to fire gilding, several hours are required. When the liquid is exhausted of 

 its gold, fresh oxyd is added, by which a further precipitation of oxyd of iron 

 is produced. The gilding obtained by this process admits of being burnished, 

 and of undergoing all the operations employed to produce mat, or dead gold. 

 One of the most difficult problems to solve in this branch of manufacture is 

 the production of dead surfaces. Its production in the ordinary way is always 

 accompanied with a loss of metal, inasmuch as it necessitates a system of cor- 

 rosion of the surface by chlorine. By Briant s process a matted surface can 

 be obtained by galvanic agency not inferior to the best of Paris, while it does 

 not require any of the subsequent operations required in fire gilding. The 

 mat appearance is spontaneously produced as soon as the coating of gold has 

 acquired a certain thickness ; it is most beautiful when the operation is car- 

 ried on in the cold. By a very simple artifice a more or less reddish tint, on 

 the one hand, or a whitish one on the other, is produced ; it is merely required 

 to dilute the bath with more or less water. "When the objects to be gilded 

 are polished or brilliant, the electro-gilding will also be brilliant, and it re- 

 quires a longer time and a thicker coating of gold to produce a deadened sur- 

 face. It is therefore important to communicate, in the first instance, a dead- 

 ened surface to the objects by the process employed in fire-gilding ; or, more 

 economically, by covering them at once with a thin pellicle of copper by the 

 electric agency, which, as is well known, produces a beautiful matted surface. 

 When any part of the object is to be protected from the action of the gilding 

 process, the choice of the substance to be used in "stopping out" these parts 

 is of importance, for it must be remembered that the bath is alkaline ; for this 

 purpose plaster, impregnated with an alcoholic solution of lac is recommended. 

 Bulletin Societe d 1 Encouragement. 



ARTIFICIAL PEODUCTIOIST OF SILICATES AND ALL T MINATES. 



By bringing chloride of silicium and other volatile chlorides in contact with 

 lime and other bases at a red heat, decomposition occurs, and silicic acid is 

 produced and is deposited in crystals, either alone or in combination with the 

 bases present. By means of lime, magnesia, alumina or glucina, and chloride 

 of silicium, crystallized quartz is obtained in its usual form, and part of the 

 base is converted into a silicate. With lime Wollastonite (table spar) is obtained 

 in rhombic tables, with two faces replacing the obtuse angles, exactly as in 

 the natural crystals. These tables are frequently united in the form of a cross 

 like the crystals of staurotite. By means of magnesia, peridote is obtained, in 

 rectangular prisms. Alumina gives a silicate in long prisms with an oblique 



