226 KOENIG—ARTIFICIAL PRODUCTION OF ORYSTALS. [June 1, 
thick tabular type, has not been fused. Zone 4th(@). A collar of 
bristling hexagonal plates, some with prismatic and pyramidal 
faces, but withal belonging to the thin type. This collar of crys- 
tals looks jet-black, the contrast with the bright gray both striking 
and beautiful. In different light the crystals always appear black, 
only in reflected light the color is gray. This zone marks the mini- 
mum of temperature at which combination of copper and arsenic 
takes place. Zone 5th(%). Is very narrow and dull gray; it reveals 
miniature crystals of the thin type. Zone 6th (7). Shows the 
beautiful pale red color of pure copper. Evidently arsenic vapors 
surrounded this part of the wire ; the temperature sufficed to let this 
arsenic combine with the oxygen of the surface, and thus give the 
latter the pure copper color, the peroxyd subliming. Next to this 
we find the wire with the usual red color due to a thin film of 
cuprous oxide. 
ad. A piece of quartz two inches long and just wide enough to go 
into my largest combustion tube, that is three-fourths inch, had a 
number of native copper crystals, pseudomorphous after quartz. 
This specimen was incubated. A growth of thick tabular domey- 
kite crystals formed all over the one side of the quartz. The arti- 
ficial nature is disguised by the quartz and the epidote in the asso- 
ciation to such an extent that any mineralogist would take it as a 
thoroughly natural production and hence a most unique specimen. 
2. ACTION OF ARSENIC VAPORS UPON ALLOYS OF COPPER, NICKEL 
AND CoBALT—MOHAWKITE, KEWEENAWITE. 
An alloy was made of the three metals in about the same propor- 
tion in which they are found in the natural mohawkite, that is 
Cu = 74 
Ni = 21 
coq 5 
100 
The alloy was cast into a bar one-fourth inch wide, and parts 
of this bar were successively exposed in the incubator under differ- 
ent conditions of temperature, of rapid or slow evaporation of 
arsenic. 
First Experiment, December 18, 1900.—The alloy is converted 
into filings and these are put directly against the plug P in the 
