I 1 .1 :< TUOPLATINQ AXD ELECTROTYPIXO. 171 



lion of the internal carcase, and this improvement has rendered 

 the Lenoir process perfectly practical. 



In both cases, with platinum as well as with lead, care must 

 l taken to leave an opening at the top, so as to allow of the 

 escape of oxygen which is constantly liberated round the wires, 

 and a second opening at the bottom to allow of the liquid being 

 constantly renewed. 



QUALITIES OF GALVANOPLASTIC COPPER. The deposited 

 copper being chemically pure is not so alterable as the mer- 

 chantable copper and alloys generally used in industry. 



Its resisting power to tensile strain is greater by 20 per 100 

 than that of cast copper. 



Its density is less than that of laminated copper and greater 

 than that of cast copper, the densities of these various materials 

 being 8 '95, 8 '75, and 8 '85 respectively for the laminated, the 

 cast, and the galvanic copper. 



2. ELECTROTYPING. 



ELECTROTYPES. Electrotyping comprises a series of me- 

 chanical or electrical means for reproducing engravings or 

 typographical compositions. 



The reproductions are called electros and electrotypes. In 

 order to produce an electro the original must be moulded and 

 the mould coated with a galvanic deposition ; a fusible metal 

 is then run at the back of this deposition so as to strengthen it, 

 and the plate thus obtained is mounted on a piece of wood of a 

 determined thickness. 



MOULDS. The first operation naturally consists in taking 

 the impress of the engraving to be duplicated. Gutta-percha, 

 or impermeable plaster, or one of the following mixtures may 

 be used for the purpose : 



I. White wax 200 grammes. 



Spermaceti 30 



Stearine 250 



Plumbic carbonate 30 



II. Glue 400 



Treacle 100 



