XI. APPLICATIONS. 331 



upon the perforated shelf of the outer cell for the purpose of keeping up the 

 strength of the solution. 



1731b. Bunsen's Battery. J. How and Co. 



This consists of a negative element of carbon contained in a vessel of porous 

 earthenware, which is surrounded by a cylindrical zinc positive element in an 

 outer glazed earthenware cell. It is charged by placing concentrated nitric 

 acid in contact with the carbon, and dilute sulphuric acid in contact with the 

 zinc. The zinc is required to be kept well amalgamated. 



li 1731c. Glass Decomposing Cell. 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 Daniell's) 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 des Arts et Metiers. 



17 32 a. 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 proofs. 3. To effect, upon the copper plate, correcting 

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



1732b. An Electrotype Apparatus, with stand, and Pog- 

 gendorff's silver voltameter. Prof. Hittorf, Munster. 



The vessels serve in investigating the processes by which the electrolytes 

 in aqueous, alcoholic, &c. solution afford passage to the electric current. They 

 make possible the keeping distinct of the changes occurring in the electrodes, 

 and fully determining them by quantitative chemical analysis. In soluble 

 electrolytes the ions can be certainly determined, and so the primary decom- 

 positions distinguished* from the secondary. Further, the apparatus shows 

 the ratio of the velocities with which the two ions move in opposite directions. 

 (See Poggendorf's Annalen, Bd. 89, 96, 103, and 106.) 



