5o8 CHAPTER XXV 



It follows then that the polarization of a product containing reducing 

 sugars depends on the quantit}' of basic lead acetate used in the clarification, 

 and it is for this reason that formal instructions often specify : " Carefully 

 avoiding an excess." Nevertheless, both the personal equation of individual 

 operators and also the composition of the lead solution will affect the deter- 

 mination ; one analyst will use just sufficient lead to obtain sufficient de- 

 colorization to enable a reading to be obtained, and a second will aim at ob- 

 taining the maximum decolorization. Lower readings will be obtained by 

 the former, and results between different analysts are not strictly comparable. 

 Elimination of this source of error is given under " Determination of Sucrose." 



Preparation of Sugar Materials for Polarimetric Observation. — Except in 

 special cases, all sugary materials require clarification and filtration before 

 observation in the polariscope. The agents used are : — 



Alumina Cream. — Used in sufficient quantit}', alumina cream will entangle 

 the colloids even in a material such as waste molasses. Its use is limited 

 to the removal of turbidity from high grade materials. It is prepared by 

 precipitating a cold saturated solution of an alum with ammonia and washing 

 the aluminium hj^'droxide by decantation till it is free from sulphates. 



Alternatively, the washing may be dispensed with and soluble sulphates 

 left in solution. This preparation is used in combination with lead 

 clarification, the sulphates precipitating any excess of lead and producing 

 perhaps a more brilliant filtrate. 



Kieselguhr. — The diatomaceous earth mined and used as kieselguhr has 

 the property of entangling colloids and affording a clear filtrate when used 

 in sufficient quantity with sugar products. It is used chiefly as an adjuvant 

 with other materials. 



Precipitation of Alumina ivithin the Solution. — This method is due to 

 the writer, and, as finally formulated, is as below : — 



A saturated solution of baryta* is prepared. At 27-5 C. such a solution 

 is nearly 0-5 normal. 165 grams of aluminium sulphate {Al2{SO^)^i8H20), 

 and 135 c.c. of normal sulphuric acid are dissolved in 1,000 c.c. This solution 

 is adjusted until 15 c.c. are exactly equivalent to 25 c.c. of the baryta solution, 

 using phenolphthalein as indicator. The sulphuric acid is employed so as 

 to accelerate inversion when sucrose is determined, as opposed to polarization. 

 As a clarificant it has no objective, but its presence avoids the use of two 

 sulphate solutions. 



The sugar material to be prepared for examination is dissolved in 50 c.c. 

 of water ; 25 c.c. of the baryta solution added and mixed with the sugar 

 solution ; 15 c.c. of the alum solution is then allowed to flow into the mixture 

 with constant stirring. The whole is then completed to 100 c.c. and is then 

 ready for filtration and examination. The volume occupied by the precipi- 

 tate produced is approximately 0-70 c.c. These quantities are sufficient 

 to clarify 3 • 25 grams, or one-eighth normal weight of a waste molasses and 

 to give a filtrate readily capable of observation in a 40 cm. tube, provided a 

 nitrogen-filled tungsten filament lamp is used. Juices and normal weights 

 of sugars can be clarified with less of the re-agents, but it is convenient to use 

 one fixed quantity and apply one fixed correction for the precipitate volume. 



*The use of aluminium sulphate and baryta as a defecant in manufacture was suggested by Pimienta in "Manuel 

 de Cultivo de Cana de Azucar." 1881. 



