124

QUANT IT A 7V V'K A(JlU('l>LTl'RAL A A* A

i f

The Polarimeter.—Listed in what (perhaps somew]
trarily) may be regarded as the order of relative import*
not in the order in which they are fixed in the insl run
essential parts of an instrument for measuring optical rot
as follows:

(a) An optical part, F, (Fig. 37) for polarizing
monochromatic light in a definite plane. This is the " p<

(6) A part, A, similar to the polarizer, which can I
in the path of the light and rotated about the axis of pro
of the beam. This is the "analyze*." With flic*
fixed in position there will be a corresponding posit io

1 l\

^zr-jr

//vx^i f |

i v
"-*-1*-- " ——--•* \l

IP S
A

PIG. 37.--- -DiaKrainmaUf! re pn '.Mentation
of thr rflW-niinl part

a nirn pic polariim't.4
•r.

analyzer which will permit the maximum brightness c
mittecl light and another which will cause total extinct
first representing a coincidence of the planes of poll
of polarizer and analyzer, the second an inclination of
these planes.
(c) A tube, S, to contain the solution under in vestigatk
can 1)0 placed in the light path, between the analyser
polarizer. This tube must bo of definite length and if nil
plane, transparent ends, placed perpendicularly to the ii
of light travel.
(d) A lens, /, for directing parallel light into the* inst
(e) A system of lenses, T, through which the operal
observe the action of the first four parts,
(/) A circular scale upon which is indicated tin:* angle i
which the analyzer is rotated.
The relative positions of these parts arc* shown in Kig.
Making a Reading.—-Briefly .staled, the detennina
rotatory power with the most simple instrument possible w
made as follows:
The analyzer is brought into a relation with the pr;
such as to permit the maximum transmission or exfinc:
light. This establishes the aero point of the instrument