DETERMINATION OF SUGAR AND STARCH. 



95? 



with petroleum ether until free from fat. The filtrate and washings are received in 

 a weighed flask, in which the fat is weighed, after recovering the petroleum ether 

 by distillation and drying the residue to constant weight at 100 C. in a water oven. 

 The fat obtained is clear, of slightly yellowish color, and undergoes appreciable 

 oxidation only on prolonged heating under the conditions mentioned above. An 

 ordinary air bath is usually too small for the proper heating of a vessel of the size 

 required. Taking the density of the insoluble portion as 1.000, and ignoring the 

 small amount of residue decanted with the 100 cc portion, the following table of 

 corrections is applicable to the per cent of fat obtained by the above method: 



When the sample contains 

 approximately 



per cent from the result 

 obtained. 



Determinations of fat are very quickly made by this method, and the results are 

 sufficiently accurate for ordinary purposes. 



Determination of sugar. A determination of the amount of sugar added in the 

 process of manufacture is readily made, by means of the polariscope, to within one 

 or two per cent of the truth; a closer determination is neither very easy nor very 

 important. The gum (see page 941) gives the aqueous solution of normal cocoa a 

 slight rotatory power, equivalent to 0.3 to 2.0 per cent of sugar in the bean in sev- 

 eral samples tested; the presence of starch necessitates the use of cold water, of 

 which 500 cc or more are necessary for the complete removal of the sugar from 

 13.024 grams of material. Considering these facts, the following method will be 

 found satisfactory for most purposes: 13.024 grams of material are placed in a small 

 mortar and triturated with alcohol until .1 smooth paste is obtained; this is trans- 

 ferred to a 500 cc flask, diluted with 400 to 450 cc water and shaken occasionally for 

 three to four hours ; 10 cc of a saturated solution of normal acetate of lead are added 

 and the volume brought to 500 cc. After standing for about one hour, with occa- 

 sional shaking, the solution is filtered and polarized in a 400 mm tube. The per 

 cent of sugar is then obtained by the following formula, in which R = the polari- 

 scopic reading, when the normal quantity for the polariscope used is 26.048 grams: 



11 



I 500- 



( 13.024 



5 R X 13.024 



Too" 



100 



: % sucrose. 



A portion of the solution, as prepared for polarization, was freed from lead and 

 tested with Fehling's solution for reducing sugar, the result being taken as an indi- 

 cation of the quality of the sugar used in the manufacture of the sample. 



For a more exact determination of the sugar, a gravimetric determination of the 

 reducing sugars in the aqueous extract, before and after inversion, is recommended. 

 (Weight of copper obtained after inversion) (weight of copper obtained before in- 

 version)=weight of copper equivalent to cane sugar present. 



Determination of starch. Mr. K. P. McElroy devised the following method for the 

 determination of starch : 



Five grams of chocolate were weighed into an Erlenmeyer flask, wet with alcohol, 

 and 30 to 40 cc of water added. The flask was then shaken at intervals until all 

 sugar present had gone into solution. Fifteen cc of a saturated solution of neutral 



