( 222: ) 
on so as to produce a sharply outlined design on the brass- and 
bronze-slides. 
That to no other cause any difference might be attributed, all slides 
were finished off in exactly the same way as had been done for the 
acid-etchings of Prof Brnrens; the etching standing out much stronger, 
this soon proved to be entirely superfluous and so the slides were 
filed only with a smooth-file. The first experiment was taken with a small 
piece of cast-brass, which proved to be composed of 58.5 °/, of copper, 
40.5 °/, of zine, also traces of lead and of tin being found. For half 
an hour it was submitted to electrolysis, the density of the current 
being + 2 amp. p. dM’. The result of this experiment is reproduced in 
fig. 1. The indented structure is very distinctly visible, there being 
in the slide besides a marked difference in colour between the crystal- 
formation and the encompassing ground-mass. Bright yellow, the crystals 
stand out from the enclosing mother-water. 
When a second experiment was taken the same alloy was submitted to 
electrolysis for 12 hours. Under the anode a glass-cup filled with 
glycerine and with oxide of magnesium was placed to catch up the 
erystals that might be hollowed out by electrolysis and which will be 
caused to sink by their weight, for as was to be expected (a thing which 
was proved by the experiment) the crystals having a higher percentage 
of copper than the mother-water (in which zine prevails) will be better 
proof against electrochemical influence and so in the end get isolated 
and detached. The residue left in the glass-cup was washed out with 
aleohol it being found that without this precaution the crystals, that 
had got detached, easily corroded, leaving nothing behind but a green 
powder; they were then dried in ether; the residue proved to contain 
1.78 mG. metal-crystals. Although these crystals had not got loose 
entirely intact, they were distinctly angular in form and showed facets. 
Being submitted to electrolysis (I wish to thank Mr. Vermass for 
his assistance in this) these crystals were found to contain 1.19 mG. 
of copper, equal to a copper-percentage of 66.8°/,. Traces of lead were 
found on the anode and proved to be PbO, but the quantity was 
too small to permit weighing. 
The second design is of a piece of plate-brass, of which the ground 
slide is in my possession. Etching and colouring after perfect grinding 
and polishing, had yielded no result. The result of half an hour’s 
electrolysis with a current of the same density as with the first expe- 
riment, and the same fluid as electrolyte, is shown in the adjoined photo- 
gram. Also the effect of the mechanic treatment can be distinctly noticed. 
Everywhere in the slide twin-erystals are to be found, which as 
Prof. Brurens explains in his work, are apt to be formed in conse- 
