XII. SPECIAL COLLECTIONS. 381 



1731c. Glass Decomposing Cell, used in the Electro- 

 type process. J. How and Co. 



Consists of a glass vessel fitted with two insulated brass bars, with attached 

 binding screws. A piece of sheet copper is hung upon one of the bars, and 

 the object to be coated on the other. The vessel is nearly filled with a strong 

 solution of sulphate of copper. The zinc pole of a battery (say DanielPs) is 

 connected with the bar to which the mould or object to be coated is attached, 

 and the copper pole to that upon which the sheet copper is suspended. This 

 apparatus will also answer for depositing silver and gold. 



1732. First Electrotype Reproduction obtained by M. 

 Jacobi. Conservatoire dcs Arts et Metiers. 



1732a. Ten Copper Plates, engraved by the electro-chemical 

 process, the proofs from which are in the accompanying album. 



Erhard, Paris. 



A proof, fresh printed from a lithographic stone, or an autograph, or a 

 proof from a copper plate wanting to be renewed, is by this process transferred 

 to a copper plate, and produces in a few moments an engraving en creux as 

 clear as that from the original plate, which is in no wise damaged by the 

 operation. By this process it is possible : 1. To avoid having to preserve 

 stones, at once brittle and cumbersome. 2. To reproduce a worn out plate, 

 and so secure unlimited copies. 3. To effect, upon the copper plate, correc- 

 tions not feasible upon the original plate worn out by previous printings. 



1732c. Electric Multiplier. Prof. George Fuller, Belfast. 



XII. SPECIAL COLLECTIONS OF APPARATUS. 



4566. Photographs of collection of Apparatus formerly 

 belonging to Volta. 



Liceo Volta of Como, Cabinet of Physics and Chemistry, 

 Prof. Giovanni Gambara. 



1. Small voltaic pile. 



2. Small voltaic pile with circle of cups. 



3. Electrophorus. 



4. Two wooden discs covered with silk. 



5. Electroscope. 



6. Apparatus for igniting hydrogen gas by the electric spark. 



7. Glass electrical pistol of Volta. 



8. Eudiometer of the same. 



9. Small squares of zinc and copper for generating electricity. 



10. Glass tube containing mercury, for determining the coefficients of the 

 expansion of air. 



11. Small case made expressly for the protection of the above instruments. 



1733. Original Apparatus with which Faraday obtained 

 the Magneto-Electric Spark. 



The Royal Institution of Great Britain. 



