NON-TEANSFER OF ELEMENTS. 



75 



mode of Suspending Objects for Coating. In beginning to operate 

 in the art of electrotyping, the student often pauses, and asks the 

 question, What is the best position in which 

 a medal should be hung in the solution ? 

 Convenience has brought into general 

 practice the suspending of it perpendicu- 

 larly in the solution, having the positive 

 electrode or pole facing it in a parallel 

 direction; but to this method there are 

 some objections. If, for instance, the 

 porous diaphragm, or single-cell system 

 be used, for obtaining the medals, it is 

 found that upon the lower portion of the medal the deposition is 

 much thicker than upon the upper portion. Indeed, when even 

 ordinary attention is not paid, the lower part becomes not only 

 thicker, but studded over with round nodules of copper, or with 

 lines composed of these nodules, while the upper part remains thin, 

 and is covered over with what is termed the sandy deposit copper, 

 in dark brown grains, capable of being rubbed off with the slightest 

 friction. No doubt this is in a great measure prevented by 

 agitating the solution ; but it is inconvenient, and requires constant 

 attention. 



If a separate battery is used, and the deposition of the medal is 

 effected in a separate vessel, by having a copper positive electrode, 

 the same inconvenience takes place to a greater or less extent, 

 according to the distance at which the two poles are placed. These 

 inconveniences are known to all electrotypists, and the cause is 

 ascribed to the different densities of the solution. The reason why 

 the solution becomes of different densities is easily understood in the 

 single-cell process: there being no copper pole to maintain the 

 strength of the solution, as it becomes exhausted of copper by the 

 deposition, the lighter portion floats on the top, and the heavier por- 

 tion remains below ; and although crystals of sulphate of copper be 

 suspended in the solution, as they dissolve they sink by their gravity, 

 and cause a flow upon the lower portion of the medal, and conse- 

 quently a much more powerful deposit. But why the same should 

 take place with a separate battery, where there is a positive elec- 

 trode of copper being dissolved, just in proportion to the copper 

 extracted from the solution by the medals has but recently been 

 discovered. 



Non-Transfer of Elements. In papers read upon this subject 

 before the Royal Society, and also before the Chemical Society, 1 it 



1 Philosophical Transactions, Part 1, for 1844; and Memoirs and Proceedings of 

 the Chemical Society, Vol. iii. page 53. 



