520 



CHAPTER XXV 



[Sucrose +3. 392 grams of NH4C1= + 99-43° S ; (13 grams of invert sugar+3-392 grams of NH4CI) x2= —33-91° S] 



Example. — Twenty-six grams of a sample were dissolved in 300 c.c. of 

 solution. Two 75 c.c. portions were taken, prepared for direct and invert 

 polarization, respectively, and finally made up to 100 c.c. The direct 

 polarization multiplied by 300/75 =4 proved to be 38-75. The invert 

 polarization multiplied by 4 was — 16 • 22 at 22 • 4° C. P — P' was thus 54 • 97. 

 Since the original sample was in i /3 normal solution the actual concentration 

 of sucrose was proportional to 1/3 X {P—P') or 18-32. Opposite 18-32 and 

 under the column " 75 c.c. taken " we find the divisor to be 132-63. This is 

 diminished by 1-27 for the temperature correction to give 131-36, which 

 divided into 54-97 gives 41-85 per cent, sucrose. 



Other Inversion Methods. — There are two other inversion methods which 

 fulfil all the postulates demanded for accuracy. These are the method of 

 inversion by invertase first suggested by KjeldahP^ and the alumina-baryta 

 defecation method of the writer- The former method has been developed 

 by O'Sullivan^^, Hudson^* and Ogilvie^^ and the routines of the two last 

 named are given here. 



As carried out by Ogilvie, the sugar material is dissolved in 200 c.c- of 

 water : 100 c.c. of this solution is treated with sulphurous acid to precipitate 



