1903.] KOENIG—-ARTIFICIAL PRODUCTION OF CRYSTALS. 23] 
The silver-white zone under the crystals demonstrates to the eye 
the difference in the ionic mobility of copper and silver. One sees 
how the copper is drawn away from the silver. It would be of in- 
terest to know whether the outermost crystals carry less silver than 
those nearest the metallic base, but as this gain of knowledge would 
also involve a destruction of the specimen I abstained, satisfied with 
the average result as exhibited in the above analysis. 
Lxperiment of February 24, 1901.—An alloy of 1 copper with 1 
silver was made and a piece weighing about 5 grams was exposed in the 
incubator for fourteen hours (overnight). The front and upper sur- 
face of the ingot was found covered with crystals. They are not good, 
but they show distinctly the habitus of the thick tabular domeykite. 
There is no tendency to rise ; the silver is evidently as little mobile 
as the nickel and acts depressingly upon the activity of the copper. 
The crystals are laterally grown together, forming a strongly coher- 
ing crust, which cracks off with the hammer blow. 
Analysis of the crust gave (0.3057 gram) : 
Atoms. 
Cr .87 = 0,88 
Ag = oot — oa t nowt 
(By difference) As = 29,12 = 0.388 
100.00 
Ratio: 
(CuAg) : As = 2.65 : 1.00 
This corresponds to a mixture of 5 (CuAg),As with 3 (CuAg),As. 
The tendency is always rather for the building up of Cu,As than of 
Cu,. 
Experiment of February 28, rg0r.—A piece of alloy 1 Cu + 1 Ag 
exposed in incubator for two days and nights at very low temper- 
ature. The end reaching towards the arsenic showed a fused, 
bluish-gray, apparently homogeneous material. At the opposite 
end are small crystals with bright faces. Habitus: steep hexago- 
nat pyramid with striated sides, capped by the normal or funda- 
mental pyramid.. 
Analysis with 0.3412 gram gave: 
Atoms. 
Cu = 4094 — 0,650 
-98 
4 Ag = 36.62 — 0.339 t es 
(By difference) As = 22.44 = 0.2992 
100-00 
Ratio: 
(CuAg) : As = 3.3: 1.00 
PROC, AMER. PHILOS. 80C. XLII. 173. P. PRINTED AUG. 7, 1903. 
