DETERMINATION OF SUGAR AND STARCH. 957 
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 ce portion, the following table of 
corrections is applicable to the per cent of fat obtained by the above method: 
60° ( 0. 24) 
55 0. 25 
50 0. 25 | 
45 0. 25 
40 | 0. 24 
: 35 -£ 0. 23 
When the sample contains } 5) | percent of fat, 0.21 \ Pex cent from the result 
approximately \ 35 ( subtract 10.19 { obtained. 
20 0. 16 
15 0.18 
10 0. 09 
a) 0. 05 
1 0. 01 J 
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 sey- 
eral samples tested; the presence of starch necessitates the use of cold water, of 
which 500 ce 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 a smooth paste is obtained; this is trans- 
ferred to a 500 ce flask, diluted with 400 to 450 ce water and shaken occasionally for 
three to four hours; 10 ce of a saturated solution of normal acetate of lead are added 
and the volume brought to 500 ce. 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: 
5 Rx 13.024 
R| 500— (yates ) 
J or 2, 
100 ee a STORE. 
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 ethos for the 
determination of starch: 
Five grams of chocolate were weighed into an Erlenmeyer flask, wet with alcohol, 
and 30 to 40 ce of water added. The flask was then shaken at intervals until all 
sugar present had gone into solution. Fifteen ce of a saturated solution of neutral 
