20 Professor Grove on a Voltaic Process for Etching 



during which the process should be continued ; and fifthly, 

 the solution to be employed. 



1st. With regard to the first element, or quantity, mainy 

 previous experiments had convinced me, that, to give the 

 maximum and most uniform quantitative* action of any vol- 

 taic combination, the electrodes should be of the same size as 

 the frenerating plates : in other words, tliat the sectional area 

 of the electrolyte should be the same throughout the whole 

 voltaic circuit. It seems strange that this point should have 

 been so generally overlooked as it has been : an electrician 

 would never form a battery, one pair of plates of which were 

 smaller than the rest; and yet the electrodes, which oifering 

 of themselves a resistance to the current, from the inoxidabi- 

 lity of the anode, are, a fortiori, a restriction when of small 

 size, have generally been formed indefinitely smaller than the 

 generating plates ; I therefore, without further experiment, 

 applied this principle to the process about to be detailed. 



2nd. The intensity of the voltaic current.— Here it ap- 

 peared to me, that, as in the electrotype, where the visible 

 action is at the cathode, a certain degree of intensity throws 

 down metal as a crystal, an increased intensity as a metallic 

 plate, and a further intensity as a pulverulent mass ; that de- 

 gree of intensity which would show on the negative deposit 

 the finest impressions from the cathode, would also produce 

 on the anode the most delicate excavations, and consequently, 

 an intensity which would just fall short of the point of evolving 

 oxygen from the plate to be etched, would be the most likely 

 to succeed ; this point was not, however, adopted without 

 careful experiment, the more so, as in one instance Mr. Gas- 

 siot succeeded in procuring a very fair etching with a series 

 of ten pairs of the nitric acid battery ; however, the results 

 of repeated experiments, in which the intensity has been va- 

 ried from a series of sixteen pairs to one of the nitric acid 

 battery, were strongly in favour of the above idea, and con- 

 sequently, went to prove that one pair gives the most efficient 

 degree of intensity for the purpose required. 



3id. The distance between the plates. — As it was proved 

 by De la Rive, that in an electrolytic solution, when the elec- 

 trodes are at a distance, the action extends a little beyond the 

 parallel lines which would join the bounds of the electrodes, 

 and thus, that the current as it were diverges and converges, 

 it appeared advisable to approximate the electrodes as nearly 



• I say quantitative action ; for, wiiere great intensity is required, as in 

 decomposing alkalis, &c., it may be advisable to narrow the electrodes, so 

 as to present a smaller surface for the reaction of the liberated elements. 



