136 
ELEMENTARY CHEMICAL MICROSCOPY 
instrument is first set so that all the reference marks take the 
same positions as when the spectroscope was first adjusted. 
Measurements of line or band positions are made by bringing 
the bright white triangle to such a position that the line or the 
edge of the band bisects the acute angle of the triangle. The 
scale S and drum g are then read and recorded. S reads from o 
to 10, g in hundredths of S. For example, in the instrument 
illustrated: Fraunhofer c = 0.42, D = 1.41, G = 7.11, etc. 
In calibrating by means of the Fraunhofer lines direct sunlight 
should be thrown into the instrument by means of the microscope 
mirror. For bright lines, hold the instrument clamped securely 
in place on a suitable clamp stand and direct it toward a Bunsen 
burner flame into which the metallic salts are to be introduced. 
The following lines will be found convenient for the calibration: 
Line. 
Corresponding 
wave length in 
Angstrom units. 
Line. 
A. 
7600 
F 
Ka. 
7682 
a. 
7201 
B. 
6870 
Cs /3 
6708 
1 d . 
C. 
6563 
G . 
Na (D). 
5893 
9 . . 
Baa. 
5535 
Rhfi . 
T 1 . 
5350 
Rba. 
E. 
5270 
h . 
h. 
5183 
Hi. 
62. 
5173 
! 
Corresponding 
wave length in 
Angstrom units. 
4681 
4607 
4555 
4593 
4383 
4308 
4226 
4215 
4202 
4103 
3968 
When only approximate resultsGn terms of wave lengths are 
needed, a very convenient device consists in plotting the curve 
for the spectroscope upon coordinate paper, using wave lengths 
as ordinates and scale divisions as abscissas. Such a calibration 
curve is shown in Fig. 68, the black dots indicating the measure¬ 
ments actually made. 
For the study of the absorption bands of liquids under the 
microspectroscope, the most convenient cells will be found to be 
tubes of different size bores and lengths whose ends are ground 
true at right angles to their axes. A piece of compact cork pro¬ 
vided with a central orifice is cemented to a glass object slide by 
