18 HISTORY OF ELECTRO-METALLURGY. 



or two of which we will refer to here, and will give the others 

 while detailing the processes to which the improvements were 

 applied. The first was the use of plumbago or black lead, to give 

 the surface of non-metallic bodies a conducting property. This 

 was the discovery of Mr. ROBERT MURRAY, a gentleman of high 

 attainments and unassuming manners, who communicated the 

 process to the members of the Eoyal Institution orally. The 

 Society of Arts afterwards awarded to Mr. Murray a silver medal, 

 as an expression of their sense of the value of the discovery. This 

 application at once freed electro-metallurgy from every bond: it 

 was no longer necessary to use either metallic moulds, or moulds 

 having metal reduced upon their surfaces by chemical means 

 which, according to the processes then known, was both tedious 

 and uncertain, and only applicable to certain substances. Plumbago 

 possessed all the requisite properties : it was convenient, plentiful, 

 and cheap, easily applied, and equally effective for every substance 

 on which the electrotypist desired to obtain a deposit, or which he 

 could wish to cover with metal, either for useful or ornamental 

 purposes. 



Separate Battery. The second improvement to be noticed is one 

 that must have followed the original discovery very soon, namely, 

 the application of a separate battery for the purposes of deposition. 

 This was suggested by Mr. MASON. Although those instances of de- 

 position of metals which have been referred to in the early history of 

 galvanism were effected by means of separate batteries, namely, by 

 placing the ends of the wires attached to the terminals of the battery 

 in the solution to be decomposed, still the discovery under considera- 

 tion was made by means of what is termed the single cell. It con- 

 sisted in simply attaching by a wire the article upon which a deposi- 

 tion was to be made to a piece of zinc, and immersing the zinc in 

 diluted acid, and the other article in a solution of the metal to be 

 deposited ; the two liquids being separated by a porous partition, or 

 diaphragm, such as moist bladder, or un glazed porcelain. In this 

 case the whole electricity was expended within the cell, to deposit 

 the metal within the mould. By Mr. Mason's discovery, the elec- 

 tricity generated in the cell could be made to do an equivalent of 

 work in a separate cell as well making the original arrangement 

 the generating cell or battery to the second cell. In this last cell was 

 also a solution of a metal having in it a sheet of similar metal 

 attached to the copper of the first cell, and the mould to be covered 

 was attached to the zinc of the first cell. Fig. 1 is an illustration of 

 Mason's improvement, which consisted in causing a medal, in the act 

 of being deposited, to serve as part of a battery for the deposition of 

 another medal. 



O 2 , Outer vessel filled with sulphate of copper. O l , another vessel 



