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 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.