by
the neck with the thumb and finger, and the bulb not handled during
this operation. Care must be taken that no particle of the sugar or
solution is lost. To determine if all the sugar is dissolved, the
flask is held above the level of the eye, in which position any
undissolved crystals can be easily seen at the bottom. The character
of the solution is now observed. If it be colorless or of a very light
straw color, and not opalescent, so that it will give a clear
transparent liquid on filtration through paper, the volume is made up
directly with water to the 100 c.c. mark on the flask. Most sugar
solutions, however, will require the addition of a clarifying or
decolorizing agent in order to render them sufficiently clear and
colorless to polarize. In such case, before making up to the mark, a
saturated solution of subacetate of lead is added.

The quantity of this agent required will vary according to the quality
of the sugar; for sugar which has been grained in the strike pan and
washed in the centrifugals, from 3 to 15 drops will be required; for
sugar grained in the strike pan but not well washed in the
centrifugals, that is, sugar intended for refining purposes, from 15
to 30 drops will be required; for sugar not grained in the strike pan,
that is, "wagon" or "string sugar," "second sugar," etc., from 1 to 3
c.c. will be required. After adding the solution of subacetate of lead
the flask must be gently shaken, so as to mix it with the sugar
solution. If the proper amount has been added, the precipitate will
usually subside rapidly, but if not, the operator may judge of the
completeness of the precipitation by holding the flask above the level
of the eye and allowing an additional drop of subacetate of lead to
flow down the side of the flask into the solution; if this drop leaves
a clear track along the glass through the solution it indicates that
the precipitation is complete; if, on the other hand, all traces of
the drop are lost on entering the solution, it indicates that an
additional small quantity of the subacetate of lead is required. The
operator must learn by experience the point where the addition should
cease; a decided excess of subacetate of lead solution should never be
used.

The use of subacetate of lead should, in all cases, be followed by the
addition of "alumina cream" (aluminic hydrate suspended in water)[2]
in about double the volume of the subacetate solution used, for the
purpose of comp