( 221 ) 
in the etching-process, I will just remark that a slight experiment, 
Le, by putting the zine into the fluid, without letting the cell give 
a current, was sufficient to prove that the eteh-desien obtained in 
the first case, stood out in much stronger relief than had been the 
case, when exclusively applying acids. 
As in any electrolytical process anions are formed which together 
with the metal of the electrode may produce dissoluble salts, 
it was important to find out what disturbing influence this would 
have, and combine with it an examination into the practicability 
of this etching method and see whether it could replace the 
one of Prof. BerreNs, in case the results might be unsatisfactory. 
The corroding influence of acids having to be avoided as much as 
possible, preference has been given to use the electric current of a 
battery instead of producing it within the apparatus itself, as happens 
in any cell. The apparatus was constructed as simply as possible 
and is exactly the same as that used for ordinary electrolytical 
experiments. 
The object that was to be etehed was used as anode (the place 
where the electric current enters), whereas a piece of copper-plate 
serves as cathode. The electric current was furnished by an accu- 
mulator-battery, having a terminal voltage of 4 volts. In etching alloys 
of copper, it proved recommendable, every time to connect two appa- 
ratuses in series or in some other way to diminish the potential 
difference, on account of the highly fleeey deposit on the cathode. As 
electrolyte, water was used to which for every 100 em? + 6 drops 
of diluted sulphuric-acid had been added, in the first place better to 
conduct the electric current; in the second place, as much as possible, 
to prevent the formation of base metal-deposits *). Of course a controll- 
ing experiment was taken by hanging a second piece of the alloy, per- 
fectly alike, in a fluid of which the percentage of acid was the same, 
in order to be able to eliminate etching by the acid. I have prefer- 
red to begin experimenting with copper-tin- and copper-zinc-alloys on 
account of the sometimes beautiful results obtained by the rubbing 
and polishing method. 
In most cases I melted myself the alloys to be sure of the absence 
of foreign substances, which may cause very great changes in structure. 
The metal-slides were hung to a piece of copper-wire, but precau- 
tions were taken that there was no contact between the wire and 
the electrolyte, to be sure that the metal-plate, which had to be etched, 
did its work as electrode. For half an hour the electrolysis went 
1) In alloys containing lead (babbits, type-metal, ete.) the sulphuric-acid on 
account of the indissolubleness of the sulphate of lead was replaced by nitric-acid. 
15* 
