XXV] CACAO PRODUCTS 329 



^ 24A + 0.5B . , . , 



C = :: in which 



o 



A = grams of butter fat in 5 grams of mixed fat; 



B = 5 — A = grams of cocoa fat in 5 grams of mixed fat; 



C = Reichert-Meissl number of extracted fat. 



From which the 



Q Q c 



Weight of butter fat in 5 grams of mixed fat = — j~- and the 



4.7 



Per cent of butter fat = per cent of total fat X — - — - 



23.5 



1 5 SUCROSE AND LACTOSE.— TENTATIVE. 



Prepare the sample by chilling well and shaving as finely as possible with a knife. 

 Transfer 26 grams of this material to an 8 ounce nursing bottle, add about 100 cc. 

 of petroleum ether and shake for 5 minutes. Centrifugalize until the solvent is 

 clear. Draw off the same by suction and repeat the treatment with petroleum 

 ether. Place the bottle containing the de-fatted residue in a warm place until the 

 residual traces of petroleum ether are practically expelled. Add 100 cc. of water, 

 shake until all the chocolate is loosened from the sides and bottom of the bottle 

 and then shake for 3 minutes longer. Add basic lead acetate solution from a burette 

 to complete precipitation, then sufficient water to make the total volume of liquid 

 110 cc. Mix thoroughly and filter through a folded filter. Make the direct polari- 

 scopic reading "a" in a 200 mm. tube. Precipitate the excess of lead by anhydrous 

 potassium oxalate and invert the solution as directed under VIII, 14. Obtain 

 the reading of the inverted solution. Multiply the invert reading by 2 to correct 

 for dilution "b". From the figures obtained calculate the percentages of sucrose 

 (S) and lactose (L) by the formulas 



(a-b) (110 + x) 



S = 



<1-1 + -Im)-s 



142.66- I 



in which the value of x is obtained from 

 0.79 



0.2244 fa-21d) . ,.,,," , , • ^, ■ , , 



in which the value of d is obtained from 



1 - 0.00204 (a - 21dj 



J ^ a— b 



142.66- 1 



1 6 CASEIN IN MILK CHOCOLATE.-TENTATIVE. 



It is unnecessary to de-fat the chocolate. Weigh 10 grams of the chocolate 

 into a .500 cc. Erlenmeyer flask and add 250 cc. of 1% sodium oxalate solution. Heat 

 to boiling and boil gently for a few minutes, then cool, add 5 grams of magnesium 

 carbonate and filter. Determine nitrogen in 50 cc. of this filtrate. Pipette 100 cc. 

 of the filtrate into a 200 cc. volumetric flask and dilute almost to the mark with 

 water. Then precipitate the casein by the addition of 2 cc. of glacial acetic acid 

 or 1 cc. of concentrated sulphuric acid. Make to volume, shake, filter and deter- 

 mine nitrogen in 100 cc. of the filtrate. The difference between the 2 nitrogen de- 

 terminations gives the nitrogen derived from the casein which, multiplied by 6.38, 

 gives the amount of casein present in 2 grams of the sample. 



