Ethylid 9 i “ ethylid “¢ 901 
side of the medial line. The apparent angle between the two 
axial planes, measured in the usual way, was found to be 81° 
for blue and 25° for red. The true angles soriesiiStlen « to 
these, obtained with the stauroscope, are 16° and 11° respec- 
tively. The first-mentioned angles, however, are not sufficiently 
accurate 35 serve for the calculation of one of the indices of 
refractio 
B. saaevis Hthylid tamine-ethylid 
nitrate. 
The crystals of the second, or anhydrous, variety of this 
compound belong to the triclinic system. Unfortunately the 
material which Prof. Mixter has thus far 3. 
exception cannot be relied upon within less 
han 30’ 
The crystals are quite uniform in habit, 
and figure 3 represents as closely as possible 
the common form. The crystal is placed in the position given 
in order to exhibit the close approximation to the monoclinic 
form. e¢, g, h are planes of the lower side, and a’ is Le es a. 
The angles measured on one crystal are as follow 
a (100) ,d(111) = 57°20’) a eee lig cae 10’ 
a'(100) AA(A11) = 58° 2’ ~— a (100) Ae(i11) = 64° 4’ 
g (111) Ae (111) = 65°44’ 
These angles pvint to a form having an obliquity in a vertical 
Testis of about 5°, but very slightly inclined in a horizontal] 
direction. The measurements for a wes (010) gave in ee : 
best case 90° 10’, and again 90° 20’. The variation from 90° i 
here within the possible error of observation, owing to ee 
imperfect character of the planes; the question was not decided, 
consequently, until a stauroscope examination showed that the 
plane of vibration for the light was not normal to } (010), but 
made an angie of about 18°, thus proving the ¢riclinie nature of 
the ore 
Th aa, angles, a as has been stated, are not sufficiently 
reliable t ey give the axial ratio calculated from them any especial 
Maa the sat shee mr values of the axes are, c=1'45, 5=1°98, 
=1, emihedral character of the crystal figured i is true 
at all i crystals, and the examination in_ the stauroscope 
failed to show any evidence of twinning. e crystals were 
hot suited for any further optical examinations. 
Am, Jour. Sct.—Tutrp 8 — XIV, No. 81.—Sept., 1877. 
