is entitled to
a bounty of 13/4 cents per pound (an amount nearly equivalent to the
market value of such sugar) or to no bounty whatever. It is desirable,
therefore, that the highest possible degree of accuracy should be
secured in the work, for while many sugars will doubtless vary far
enough from either of the two standard percentages fixed upon in the
act, viz., 80 deg. and 90 deg., to admit of a wide margin of error without
material consequences, yet a considerable proportion will approximate
to them so closely that a difference of a few tenths of a degree in
the polarization will change the classification of the sugar.

A very high degree of accuracy may be obtained in the optical
estimation of sugars, if the proper conditions are observed. Such
conditions are (1) accurately graded and adjusted instruments,
weights, flasks, tubes, etc.; (2) skilled and practiced observers; (3)
a proper arrangement of the laboratories in which the work is
performed; and (4) a close adherence to the most approved methods of
manipulation.

On the other hand, if due observance is not paid to these conditions,
the sources of error are numerous, and inaccurate results inevitable.

We will endeavor to point out in this report the best means of meeting
the proper conditions for obtaining the highest degree of accuracy
consistent with fairly rapid work. It would be manifestly impossible
to observe so great a refinement of accuracy in this work as would be
employed in exact scientific research.

This would be unnecessary for the end in view, and impossible on
account of the amount of time that would be required.

I.--INSTRUMENTS AND APPARATUS.

It is of the greatest importance that the polariscopes and all
apparatus used in the work shall be carefully and accurately adjusted
and graduated, and upon a single and uniform system of standardization.
Recent investigations of the polarimetric work done in the customs
branch of the Treasury Department have shown that a very considerable
part of the want of agreement in the results obtained at the different
ports was due to a lack of uniformity in the standardization of the
instruments and apparatus.

_(a.) The Polariscope._--There are many different forms of this
instrument used. Some are adapted for use with ordinary white light,
and some with monochromatic light, such as sodium ray. They are
graduated and adjusted upon various standards, all more or less
arbitrary. Some, for example,