84 METHODS OF ANALYSIS [Chap. 



100 (P - I) • u- u 



S = =^ p Fp ^ in which 



142.66 - 2 - 0-0065 [142.66 - ^ - (P 



S = per cent of sucrose; 

 P = direct reading normal solution; 

 I = invert reading normal solution; 

 T = temperature. 



Bt/ Polarization Before and After Inversion with Invertase.— Tentative. 



15 REAGENT. 



Invertase solution (Hudson Method.^)— Mix 1 kilo of pressed baker's or brewer's 

 yeast with 1 liter of tap water and 50 cc. of toluene and keep at room temperature 

 2-3 days to allow autolysis to proceed to the stage of maximum inverting activity. 

 Then add neutral lead acetate in slight excess, filter, precipitate the lead in the 

 filtrate with hydrogen sulphid, filter again and then dialyze the filtrate thoroughly 

 in a collodion sac. Preserve in an ice box the dialyzed solution with the addition 

 of a little toluene to prevent the growth of micro-organisms. Note the optical 

 activity of the invertase solution and correct the invert reading according to the 

 amount of the solution used. 



1 6 DETERMINATION. 



Dissolve the normal weight (26 grams) of the substance in water, clarify, make 

 up to volume, and take the direct polarization (P) as directed under 14. If lead 

 has been used as a clarifying agent, remove the excess of lead from the filtrate, with 

 anhydrous sodium carbonate or potassium oxalate, and filter. To 50 cc. of the 

 filtrate in a 100 cc. flask add acetic acid, drop by drop, until the reaction is acid to 

 litmus, add 10 cc. of the invertase solution, fill the flask with water nearly to 100 cc. 

 and let stand in a warm place (about 40°C.) overnight. Cool and make up to 100 cc. 

 at 20°C. Polarize at 20°C. in a 200 mm. tube. Allow the solution to remain in the 

 tube for an hour and repeat the polarization. If there is no change from the pre- 

 vious reading, the inversion is complete, whereupon the reading and temperature 

 of the solution are carefully noted. Correct the reading for the optical activity 

 of the invertase solution and then multiply by 2. Calculate the percentage of 

 sucrose by the following formula: 



100 (P - I) . ... 



in which 



142 0.0065 1142 (P 



2 L 2 



■'] 



S = per cent of sucrose; 



P =« direct reading; 



I = invert reading; 



T = temperature at which invert reading is made. 



17 DETERMINATION OF SUCROSE AND RAFFINOSE.-OFFICIAL. 



(Of value chiefly in the analysis of beet products.) 



If the direct reading is more than 1° higher than the per cent of sucrose as - al- 

 culated by the formula given under 14, raffinose is probably present. Calculate 

 sucrose and raffinose by the following formula of Herzfeld: 



