332 
POPULAR SCIENCE REVIEW. 
the series of papers on thallium which he is publishing in the u Chemical 
News,” gives the following as a simple method : — A few grains of the 
ore are crushed to a fine powder in an agate mortar, and a portion 
taken up on a moistened loop of platinum wire. Upon gradually intro- 
ducing this into the outer edge of the flame of a Bunsen gas-bumer, and 
examining the light by means of a spectroscope, the characteristic green 
line will appear as a continuous glow, lasting from a few seconds to half a 
minute or more, according to the richness of the specimen. By employing 
an opaque screen in the eyepiece of the spectroscope, to protect the eye 
from the glare of the sodium line, thallium may be detected in half a grain 
of mineral, when it is present only in the proportion of 1 to 500,000. 
The sensitiveness of this spectrum reaction is so great that no estimate can 
be arrived at respecting the probable amount of thallium present. 
New Arrangement of M. Becquerel's Sulphate of Copper Pile. — M. Trouve 
says, in the 11 Comptes Bendus,” quoted <in the 11 Chemical News,” 
that the salts of copper and zinc are simply maintained in contact 
with the metals (of the same name) by the capillary action in rolls of 
paper. The pile is very portable, has the same electromotive force as an 
ordinary sulphate of copper pile of the same number of couples, and may 
act continuously for a long time if placed in a closed vessel to obviate 
desiccation. 
What is the Opeioscope? — A late number of the 11 Lens” says that this is a 
new and simple instrument, suggested by Professor A. E. Dolbear, for the 
purpose of demonstrating the pulsations of sound. Take a tube of any 
material, from one to two inches in diameter, and anywhere from two inches 
to a foot or more in length. Over one end paste a piece of tissue paper, or 
a thin piece of rubber or goldbeater’s skin — either will do. In the centre of 
the membrane, with a drop of mucilage, fasten a bit of looking-glass not 
more than an eighth of an inch square, with the reflecting side outward, of 
course. When dry take it to the sunshine, and with the open end of the 
tube at the mouth, hold the other end so that the beam of reflected 
light will fall upon the white wall, or a sheet of paper held in the 
hand ; now speak, or sing, or toot in it. The regular movement of the beam 
of light with the persistence of vision, presents very beautiful and regular 
patterns, that differ for each different pitch and intensity, but are quite 
uniform for given conditions. If a tune like “ Auld Lang Syne ” is tooted 
slowly in it, care being taken to give the sounds the same intensity, a series 
of curves will appear, one for each sound and alike for a given sound, 
whether reached by ascension or descension, so that it would be possible to 
indicate the tune by the curves ; in other words, it is a true phonautograph. 
By trial one can find some tone which causes the membrane to vibrate in a 
single plane, and of course a straight line will appear upon the screen. If, 
while the sound is continued, the tube be swung back and forth at right 
angles to the line, the sinuous line will appear, which maybe either simple, 
representing a pure and simple sound, or it may be compound-sinous, show- 
ing over-tones, precisely as in Konig’s manometric flames. With the lecture- 
room darkened, and using the beam of light from a port lumiere or from a 
lantern, these may be projected of an immense size. There is no trouble in 
the world in making them eight or ten feet amplitude, or more if needed. 
