SULPHITE OF SILVER PLATING SOLUTION. 



107 



with the precautions stated at page 104. "When the precipitated 

 chloride of silver is well washed, some of the crystals of hyposulphite 

 of soda are dissolved, and the solution is added to the chloride of 

 silver, which it dissolves, forming the plating solution. It is not 

 necessary to crystallize the hyposulphite of soda, if used as soon as 

 made. 



The hyposulphite of silver solution is very easily decomposed by 

 the electric current, so that a weak battery will suffice to plate by 

 it : but its great objection is its liability to decompose in the light, 

 and to deposit the silver as sulphuret : unless great care is exercised, 

 the silver deposited from it will be in a granular condition, which is 

 a great objection in plating. 



Sulphite of Silver Plating Solution. The Sulphite of silver solu- 



tion is prepared in the following mariner, as described by the pa- 

 tentee of the process : 



" The solution which I use is made in the following manner : I 

 take of the best pearl-ash of commerce 28 Ibs. (avoirdupois) and add 

 to it 30 Ibs. (avoirdupois) of water, and boil them in an iron vessel 

 until the pearl-ash is dissolved ; the solution should then be poured 

 into an earthenware or other suitable vessel, and suffered to stand 

 until the liquor becomes cold. It should then be filtered, and 14 

 Ibs. (avoirdupois) of distilled water added thereto ; sulphurous acid 

 gas (obtained by any of the known processes) should then be passed 

 into the filtered liquor until it is 

 saturated, taking care not to add 

 sulphurous acid gas in excess. 

 The liquor should be again filtered, 

 and the liquor so filtered is what 

 I term the solvent, or sulphite of 

 potash. 



" To make the Silvering Liquor 

 which I use in coating with 

 silver the surface of articles 

 formed of metal or metallic alloys, I 

 dissolve 12 oz. (avoirdupois) of 

 crystallized nitrate of silver in 

 3 Ibs. of distilled water (in a cleaii 

 earthenware vessel), and add to 

 the solution, by a little at a time, 

 the before-mentioned solvent, so 

 long as a whitish coloured precipi- 

 tate is produced (care being taken 

 not to add more of the solvent than is necessary.) After the preci- 

 pitate has subsided, I pour off the supernatant liquor, and wash the 

 precipitate with distilled water. TO the precipitate I add as much 



