50 ELECTROTYPE PROCESSES. 



which there is always a deposit of copper upon the paper, thus 

 occasioning a loss. 



Common coarse garden-pots answer excellently for porous vessels, 

 closing the aperture at bottom by a cork. 



The precautions that have been given as to the preserving of the 

 porous cell, when not in use, is applicable to the cells or partitions 

 used in these processes, which, when not in use, should be kept in 

 water, or should not be allowed to dry until they have been in water 

 long enough to dissolve out the salts that were within the pores of 

 the cell ; otherwise the salts crystallize, and either crack the cell or 

 cause it to scale off in small pieces. Porous cells, when not thoroughly 

 washed and freed from salts, if laid aside for a few days, often throw 

 out an effervescence, or crystalline growth, like mould, of a soft silky 

 texture, and from one-half to one inch in length. An analysis of 

 this efflorescent matter gave 



Oxide of zinc . . . . 39 "6 

 Sulphuric . . . . 26'0 



Water 34'2 



99-8 



Comparative Value of Exciting Solutions. We have recommended 

 the porous cell being filled by dilute sulphuric acid, which we con- 

 sider best ; but other saline solutions will serve the same purpose : 

 solutions of common salt, sal ammonia, and sulphate of zinc, have 

 been recommended, and each has been called best in its turn. The 

 following results of experiments with these solutions in the porous 

 cell will show their relative qualities, and enable the student to 

 judge for himself. The size of the zinc plate in the cell measured 

 6 inches by 6 inches; the copper plates upon which the deposits 

 were formed were the same size ; the solution of copper was kept 

 at the. same strength ; the time that each was in solution was 16 

 hours. 



