The complete verification of the accurate adjustment of the
polariscope by means of three control plates, as given above, should
be employed whenever it is set up for the first time by the officer
using it, whenever it has sustained any serious shock or injury, and
whenever it has been transported from one place to another. It should
also be done at least once a week while the instrument is in active
use.

After the complete verification has been performed as described,
further checking of the instrument is done by means of one control
plate alone, the one approximating 90 deg., and the setting of the zero
point is dispensed with, the indication of the scale for sugar
solutions being corrected by the amount of deviation shown in the
reading of the 90 deg. control plate from its established value as
ascertained from the table, at the temperature of the room.

For example: A sugar solution polarizes 80.5; the control plate just
before had given a polarization of 91.4, the temperature of the room
during both observations being 25 deg. C. According to the table the value
of the control plate at 25 deg. C. is 91.7; the reading is, therefore, 0.3
too low, and 0.3 is added to the reading of the sugar solution, making
the corrected result 80.8. The temperature of the room should be
ascertained from a standardized thermometer placed close to the
instrument and in such a position as to be subject to the same
conditions.

PREPARATION OF THE SUGAR SOLUTION FOR POLARIZATION.

If the sample is not entirely uniform it must be thoroughly mixed
before weighing out, after all the lumps are broken up, best with a
mortar and pestle. Then 26.048 grammes are weighed out on the balance
in the tared German silver dish furnished for this purpose. Care must
be taken that the operations of mixing and weighing out are not unduly
prolonged, otherwise the sample may easily suffer considerable loss of
moisture, especially in a warm room. The portion of sugar weighed out
is washed by means of a jet from a wash bottle into a 100 c.c. flask,
the dish being well rinsed three or four times and the rinsings added
to the contents of the flask. The water used must be either distilled
water or clear water which has been found to have no optical activity.
After the dish has been thoroughly rinsed, enough water is added to
bring the contents of the flask to about 80 c.c. and it is gently
rotated until all the sugar has dissolved. The flask should be held