different hours of the day. For example, the room should not be
allowed to become cold at night, so that it is at low temperature in
the morning when work is begun, and then rapidly heated up during the
day. The polariscope should not be exposed to the direct rays of the
sun during part of the day, and should not be near artificial sources
of heat, such as steam boilers, furnaces, flues, etc.

The tables upon which the instruments stand should be level.

IV.--METHODS OF MANIPULATION.

The methods of manipulation used in the polarization of sugar are of
prime importance. They consist in weighing out the sugar, dissolving
it, clarifying the solution, making it up to standard volume,
filtering, filling the observation tube, regulating the illumination,
and making the polariscopic reading.

The proper conduct of these processes, in connection with the use of
accurately graduated apparatus, is the only surety against the
numerous sources of error which may be encountered. Different sugars
require different treatment in clarification, and much must
necessarily be left to the judgment and experience of the operator.

The following directions are based upon various official procedures
such as the one used in the United States custom houses, the method
prescribed by the German government, etc. They embody also the result
of recent research in regard to sources of error in polarimetric
estimation of sugar:

DIRECTIONS FOR THE POLARIZATION OF SUGAR.

1.--_Description of Instrument and Manner of Using._

The instrument employed is known as the half shadow apparatus of
Schmidt and Haensch. It is shown in the following cut.

[Illustration]

The tube N contains the illuminating system of lenses and is placed
next to the lamp; the polarizing prism is at O, and the analyzing
prism at H. The quartz wedge compensating system is contained in the
portions of the tube marked F, E, G, and is controlled by the milled
head M. The tube J carries a small telescope, through which the field
of the instrument is viewed, and just above is the reading tube K,
which is provided with a mirror and magnifying lens for reading the
scale.

The tube containing the sugar solution is shown in position in the
trough between the two ends of the instrument. In using the instrument
the lamp is placed at a distance of at least 200 mm. from the end; the
observer seats himself at the opposite end in such a manner as to
bring his eye in line with th