ELECTRUM 



valuable to be risked in the deposit- 

 ing solution, it may be used as the 

 cathode of the operation. It is pre- 

 pared by having a wire twisted 

 round its edge leaving sufficient 

 length for attaching to the ter- 

 minal of the electric battery or 

 machine. The face which is not to 

 be copied is embedded in gutta- 

 percha ; the face to be reproduced 

 is slightly greased with olive 

 oil by means of a fine hair brush, 

 to prevent a too powerful ad- 

 hesion of the deposited metal, 

 after which the medal is ready for 

 the bath. 



The solution is prepared according 

 to the metal to be deposited, usu- 

 ally copper ; after from twelve to 

 twenty-four hours the deposit will 

 have acquired the necessary thick- 

 ness, probably about O'OIS in., and 

 the medal will be removed from the 

 bath, when the electrotype may 

 be detached. If now a mould be 

 taken of this electrotype, and then 

 another electrotype taken off that 

 mould, the second electrotype will 

 be a duplicate of the face of the 

 original medal. In a similar way a 

 duplicate of the other face of the 

 medal may be obtained, when the 

 two halves may be trimmed and 

 soldered together, making a com- 

 plete reproduction of the original, 

 which may then be electro-plated, 

 if required, with any appropriate 

 metal. In this way the copies of 

 rare or historic coins and medals in 

 museums have been made. 



If the original coin or medal is 

 too precious to be risked in the 

 electrotype bath a plaster cast will 

 be prepared, or, better, a mould in 

 gutta-percha by the aid of pressure, 

 which is indeed precisely the pro- 

 cess followed in the preparation of 

 an electrotype from a forme of type. 

 The type is first thoroughly cleaned, 

 dried, and blackleaded, one object 

 of the latter being to prevent too 

 firm adhesion of the deposited 

 metal. A shallow tray is filled with 

 a molten mixture of beeswax, tur- 

 pentine, and plumbago, and the 

 surface, when set, blackleaded. The 

 forme of type is then forced into this 

 mixture by pressure and a mould 

 thus produced. This mould is 

 coated all over with plumbago, and 

 has a copper wire embedded in it 

 all round the impression which is 

 to be reproduced in order to in- 

 crease the conductivity of the 

 mould when in the bath, the wire 

 being connected with the terminal 

 of the vat, in which the mould be- 

 comes the cathode. 



The anode is a plate of copper 1 

 and the solution is copper sulphate. 

 A powerful current is used to give 

 a rapid deposition and secure the 

 necessary thickness in the shortest 

 possible time. When the electro- 



2859 



type is finished in the bath it is 

 removed and separated from the 

 wax bed by melting the latter in 

 hot water, after which it is laid face 

 down on an iron plate, heated, sur- 

 rounded by a frame of iron bars, 

 and " backing " metal poured over 

 it to a depth of from J to f in. It is 

 then trued up on a steel plate by 

 hammering till perfectly flat, 

 trimmed, and mounted on a 

 wooden block to make it " type 

 high"; or if it is to be used on a 

 rotary printing machine it is bent 

 by rollers to the required curva- 

 ture. If many impressions are to be 

 taken the electrotype so prepared 

 may be " steel faced " by having a 

 deposit of iron given to it by a 

 separate operation in the electro- 

 lytic bath. While still important, 

 improvements in the art of stereo- 

 typing have deprived the electro- 

 type of some of the value which at 

 one time it possessed. See, Elec- 

 trolysis ; Printing. 



ELECTRUM 



Electrum. Term at various 

 times applied to different materials. 

 In ancient days it was given to 

 amber, in the Middle Ages to com- 

 mon brass, in modern times to an 

 alloy of copper 8 parts, nickel 4, 

 and zinc 3'5 (sometimes the nickel 

 is 6 parts), a beautiful artificial 

 silver with a bluish tint much used 

 for the manufacture of drawing 

 and other instruments ; also to an 

 alloy of copper, zinc, and tin, and 

 to native minerals containing gold 

 and silver, the latter running from 

 20 p.c. to 50 p.c. An alloy of gold 

 and silver (15 p.c. to 35 p.c. silver) 

 known by this term, of a pale yel- 

 low colour, hence the association of 

 the term with amber, was much 

 used by the early Greeks and Ro- 

 mans for ornaments and coins ; 

 the earliest coins known were 

 made of it ; while rods having 651 

 parts gold and 334 silver in 1,000 

 were used as money in Asia Minor. 

 See Metallurgy. 



E-ectrotyping. 1. Smoothing out the wax. 2. Wax mould in position. 3. Wax 



impression from block. 4. Copper shell on mould when taken from the battery. 



5. Peeling copper shell from mould. 6. Pouring in backing of molten lead 



