OPTICAL ROTATION

123

of the ordinary applications of the polarimeter to analytical
problems the influence of these factors is negligible.

From these considerations the formula:

200 = 100 a (1)

L *D cl

is derived, as representing the specific rotation of an active
substance in solution, where a is the angle of rotation pro-
duced by a column I dm in length and of concentration c gin
in 100 cc.

A few examples, out of a very large number of optically active
substances, with their specific rotatory powers are given in the
following table, in which the sign (4-) indicates dextro-rotation
and ( —) laevo-rotation. The solvent is understood to be water,
unless otherwise stated.

TABLE IV.—SPECIFIC ROTATORY POWERS

Substance
r I 20° *
[<*]/>

Dextrose (grape sugar) .............................
4-53. 1

Levulose .
- 93 . 3

Sucrose (cane sugar) . .........
4-66.5

Invert sugar ...................................
-20.57

Lactose (milk sugar)
-1-52.53

Maltose (malt sugar) . ....
+ 137.5

Starch ....................... ..............
4-190.0

Tartaric acid (ordinary) ............................
4-12.0

Nicotine (in benzene)
— 164 0

Cocaine (in chloroform) . ........
— 16 3

Quinine sulphate (in alcohol) .....................
—225.7

Camphor (in benzene)
-1-41 4

Lemon oil (no solvent) . .
4-59 to 4-67

Orange oil (no solvent) . . ........
496 to 4-98

* These figures represent mean values for ordinary concentrationn.
There is nearly always a certain variation with concentration and when*
this is large it must be taken into consideration. For example, the Hpc
cific rotation of levulose is —88.13 — 0.2583 c, and of dextrose 4-52.50 4
0.0188 c 4- 0.000517 c2, c indicating grams of active material per 100 «<r.
It must also be noted that a number of substances exhibit "muttirotation/*
that is, the rotation of the freshly prepared solution changes after a. certain
lapse of time into the final, stable value.

1

I,