ii;i-o.-i rioN oi VARIOUS MI.IALS. 187 



to the ouode, the colorations on this plate are effected in an 

 analogous manner. If a piece of cardboard is placed between 

 the conducting wire and the plate, the colorations take place 

 unhide this improvised screen. 



The colours so produced resemble those of the prism, but as 

 they do not firmly adhere to the metal, the latter must be care- 

 fully washed with distilled boiling water, and, when dry, coated 

 with a layer of good white varnish with alcohol. 



DEPOSITION OF ZINC. 



The process of depositing zinc by simple immersion on well 

 scoured iron is generally designated by the name of galvanisa- 

 tion. This deposit, which has nothing galvanic besides its name, 

 protects iron from oxidation for a comparatively long time. 



Many attempts have been made at obtaining good deposits 

 with batteries, but we do not believe that any industrial results 

 have ever been obtained. 



The following is a process, somewhat old, described by Mr. 

 Watt : 



Dissolve 7 kilogrammes of commercial potassic cyanide in 

 100 litres of distilled water. Pour into the solution 2 '50 kilo- 

 grammes of concentrated ammonia (density 880). After stir- 

 ring and mixing well, place a few porous cells, such as DanieU's, 

 in the solution, and fill them with a concentrated solution of 

 potassic. cyanide (about 550 grammes for 5 litres of water) until 

 the levels inside and outside are even. Place in the porous 

 cells some pieces of iron or of copper connected with the 

 negative pole of a battery. Place in the solution of potassic 

 cyanide and ammonia some pieces of laminated zinc of good 

 quality, and scoured with hydrochloric acid, and connect them 

 with the positive pole of the battery. Send the current through 

 until the solution of cyanide and ammonia has absorbed about 

 2 kilogrammes of zinc, that is to say, 10 grammes per litre. 

 Then remove the zincs and the porous cells, dissolve 2*5 kilo- 

 grammes of alkaline carbonate (potash preferably) in a portion 

 of the preceding solution, and mix the whole, stirring and 

 mixing with care. Let the bath settle, and decant. 



