1903. ] WRIGHT—CRYSTALLOGRAPHIC PROPERTIES. 237 
malleable to some extent, but breaks off short when nicked with 
the chisel and then bent. Looks homogeneous. 
Analysis gave: 
Pb = 96,10 
AS 3-75 
99.85 
Pb: As ==-0.4637 : 0.050 = 9.27: 1 
The ratio is that of whitneyite. The ionic mobility is small. 
MICHIGAN COLLEGE OF MINEs, May, 1903. 
CRYSTALLOGRAPHIC PROPERTIES. 
BY FRED EUGENE WRIGHT. 
The following group of artificial minerals, which Dr. Koenig has 
kindly intrusted to me for crystallographic investigation, is charac- 
terized by high metallic luster, tin-white to steel-gray and even 
black color, conchoidal fracture and hardness : 3-4. The crystals 
obtained are all small and rarely exceed a millimeter in length. 
The character and quality of the crystal faces is not uniform for 
the whole group. Those of domeykite are usually sharp, well 
formed and furnished single reflection signals on the goniometer, 
whereby a fairly exact determination of its elements could be 
obtained. The crystals of the remaining minerals are far less per- 
fect, their uneven undulating faces evincing such indistinct, mani- 
fold reflexion signals on the goniometer that an accurate determina- 
tion of their elements was impossible. 
The crystals were measured on a Goldschmidt’s two-circled 
goniometer (model 1go1), with attachment for observing small, weak 
faces and an electric arc goniometer lamp.’ 
1The electric goniometer lamp (Fig. A) consists of a box (a2) made of Rus- 
sian sheet iron, lined with asbestos cardboard, and of an electric lamp (4). The 
bazk of the box (a) is left open to allow the insertion of the electric lamp—a 
small black movable curtain serving to shut off all false light, which might dis- 
turb in measuring. The mirror (a) and cap (e) are used to light the verniers 
and were taken bodily from a Goldschmidt’s Auer burner gas goniometer lamp 
(see Zeitschrift fiir Krystallographie, Bd, xxiii, 1894, p. 149. V. Goldschmidt. 
Eine neue Goniometer-lampe). The electric lamp (4) is the No. Io, hand 
feed, of J. B. Colt & Co., Chicago, Ill. (price, $10), together with an adjustable 
theostat (seven to eighteen ampéres, $13). By means of the latter the intensity 
