light; however, nucleic acids, proteins, and carbohydrates, all associated with life, do.
To measure the ability of a substance to rotate plane polarized light, it is necessary to place the substance between two polarizing filters. Plane polarized light passes through the substance into the second filter, which has been rotated so that no light can penetrate. Now, if the natural material can cause the plane ray to twist, some light will begin to leak through the second, or analyzer, filter. To restore the initial condition of the incident light leak, the analyzer must be rotated through a certain angle. The extent to which the analyzer is rotated is the measure of net optical rotation. Figure
Figure 12.—Optical system for optical-rotatory device.
