228 KOENIG—ARTIFICIAL PRODUCTION OF CRYSTALS. [June 1, 
The analysis with 0.0867 gram of the absolutely pure crystals 
gave : 
Cu (605402 103) Fe —— rOoe f 1.1463 
(Ni + Co) = 2.70 : 58.6 = 0,0461 ‘ 
AS ae Be as 0.3750 
100.13 
Ratio: 
(CuNi Co) : As = 3.06: 1.00 = mohawkite 
Both experiments show conclusively that nickel and cobalt will 
enter the crystals without changing the hexagonal symmetry; that 
domeykite and mohawkite are indeed isomorphous. At the same 
time the interesting fact is to be dealt with that nickel and cobalt 
do not pass into the arsenide with the copper in the ratio in which 
the alloy exposes them to the action of the arsenic vapors. That 
in fact the ionic mobility of nickel and cobalt is only approximately 
one-sixth that of the copper. For in the alloy the ratio of copper 
to nickel and cobalt is nearly 4 : 1, whilst in the crystals it is 25: 1. 
The highest percentage of Ni + Co furnished for mohawkite was 
4.51, but the analysis was otherwise unsatisfactory. 
3. ACTION OF ARSENIC VAPORS UPON NICKEL. 
Two cakes of nickel were exposed in the incubator for twenty- 
four hours. No crystals could be obtained, not even of the most 
imperfect type. A brittle material formed as a thin crust of a dull 
gray color. It was not analyzed. The action upon cobalt was 
similar. The ionic mobility of these metals under these conditions 
seems to be near zero. We may infer that in the previous experi- 
ments Ni and Co were moved by infection from the copper’s ionic 
vigor. 
4. ACTKON oF ARSENIC VAPORS UPON AN ALLOY OF COPPER WITH 
SILVER—ARGENTODOMEYKITE. 
The metals were melted together in the proportion 9:1. The 
alloy was cast into a bar and fragments of this were exposed in the 
incubator. 
Experiment of January 22, 23, 1901.—The material for action is 
a solid piece of the bar about 15 x 25 millimeters. The crystals grew 
out of this alloy towards the arsenic as rapidly as out of pure cop- 
per. They are of the tabular variety, medium thickness. The 
