82 METHODS OF ANALYSIS [Chap. 



neutral lead acetate and basic lead nitrate (Herles' solution) have been made official 

 by the Association. 



"After bringing the solution exactly to the mark at the proper temperature, and 

 after wiping out the neck of the flask with filter paper, pour all of the well-shaken 

 clarified sugar solution on a rapidly acting filter. Reject the first portions of the 

 filtrate, and use the rest, which must be perfectly clear, for polarization." It is 

 advisable to reject the first 20 cc. that run through, then cover the funnel with a 

 watch glass and use the remainder for polarization. In no case should the whole 

 solution or any part be returned to the filter. If cloudy after the 20 cc. have been 

 rejected, begin a new determination. 



"Whenever white light is used in polarimetric determinations, the same must be 

 filtered through a solution of potassium dichromate of such a concentration that the 

 percentage content of the solution multiplied by the length of the column of the solu- 

 tion in centimeters is equal to nine." This concentration must be doubled in 

 reading carbohydrate materials of high rotation dispersion, such as commercial 

 glucose, etc. 



13 PREPARATION AND USE OF CLARIFYING REAGENTS.— TENTATIVE. 



(a) Basic lead acetate solution. — Boil 430 grams of neutral lead acetate, 130 grams 

 of litharge, and 1 liter of water for 30 minutes. Allow the mixture to cool and settle 

 and dilute the supernatant liquid to a specific gravity of 1.25 with recently boiled 

 water. Solid basic lead acetate may be substituted for the normal salt and litharge 

 in the preparation of the solution. 



(b) Ahimina cream. — Prepare a cold saturated solution of alum in water. Add 

 ammonium hydroxid with constant stirring until the solution is alkaline to litmus, 

 allow the precipitate to settle and wash by decantation with water until the wash 

 water gives only a slight test for sulphates with barium chlorid solution. Pour off 

 the excess of water and store the residual cream in a stoppered bottle. 



(C) Dry basic lead acetate {Home method). — This clarifying agent is obtained as 

 a dry powdered salt and should contain 72.8% of lead, which corresponds to a com- 

 position of 3Pb(C2H302)22PbO. Dissolve the normal or half -normal weight of the 

 sugar solution in a flask with water and complete the volume. Add a small quantity 

 of the dry salt and shake, then add more and shake again, repeating until completely 

 precipitated but avoiding any excess. Of this salt 0.1346 gram is equivalent to 1 cc. 

 of the basic lead acetate solution, described under (a). When molasses or any other 

 substance producing a heavy precipitate is being clarified, some dry, coarse sand 

 should be added to break up the balls of basic lead acetate and the precipitate. 

 (This method is to have equal weight with the use of a solution of basic lead acetate 

 in clarifying cane, sorghum, and beet products.) 



(d) Neutral lead acetate. — Prepare a saturated solution of neutral lead acetate and 

 add it to the sugar solution before completing to volume. Its use is imperative when 

 determining the reducing sugars in the solution used for polarization. 



(e) Basic lead nitrate {Merles' solution). — (1) Dissolve 250 grams of lead nitrate 

 in water and make up to 500 cc. (2) Dissolve 25 grams of sodium hydroxid in water 

 and make up to 500 cc. 



Add equal amounts of (1) and (2) to the sugar solution, shake, and add more if 

 complete precipitation has not occurred, but avoid any excess. Then complete 

 the volume with water. When this solution is used for clarification, the factor in the 

 Clerget determination becomes 143.5 instead of 142.66. 



