124 Laboratory Arts 



Filter while hot, and keep both solutions in well-stoppered 

 bottles in the dark. 



The surface to be silvered must first be cleaned by 

 thoroughly washing in strong caustic potash solution, then 

 dilute nitric acid, finally in distilled water. Between each 

 washing the surface should be rubbed with a soft wet duster 

 (cheese cloth is the best material for this purpose). A solution 

 of stannous chloride in water to which a single drop of hydro- 

 chloric acid has been added is then poured gently and evenly 

 over the surface, and the object well washed in tap water, taking 

 care not to touch the prepared surface with fingers or duster 

 after the treatment with tin chloride. 



While still wet, the object is placed in a waxed dish (see 

 below), and a mixture of equal volumes of the two solutions 

 already prepared quickly poured over it, avoiding splashing and 

 air-bubbles ; and if possible avoiding a direct stream upon the 

 prepared surface. In about an hour the silvering will be com- 

 plete, when the liquid may be poured off, the article cleaned 

 and dried, and the apparatus cleaned up. 



The silvered surface should not be touched with the fingers, 

 and when quite dry may be varnished with very dilute shellac 

 varnish, but the varnishing of deposited silver is always 

 dangerous, owing to the contraction of the varnish upon drying. 



Gutta-percha dissolved in benzene is said to be free from 

 this defect, a varnish recommended for this purpose being 

 gutta percha, 5 parts by weight; gum dammar, 20 parts by 

 weight ; benzene, 75 parts by weight. 



Stains may be removed with a pad of cheese cloth dipped 

 in dilute nitric acid. 



2. The difficulty of the silver depositing upon surfaces 

 where it is not required is overcome by waxing these surfaces. 

 A porcelain dish, for example, may be heated, some paraffin 

 wax melted in it, and run round the hot dish, and the excess 

 poured off. Silver will not deposit upon such a dish. 



A convenient receptacle for silvering is easily made by 

 folding a piece of waxed paper prepared by dipping into 

 melted wax a sheet of thin unglazed writing paper until 

 bubbles cease to come away, then draining from one corner 



