it
Ml
DAIRY PRODUCTS	219
F * per cent of fat,
R = corrected reading and
r = observed reading.
Ten grams is the weight of the original undiluted sample in the solution as
finally used for polarization.
Calculate the per cent of sucrose by Clerget's formula, developed on
page 132, Part II. Taking account of the fact that less than the normal
weight of milk sample was used this formula becomes:
2_7600(a-_16)
~
S = per cent of sucrose in the sample,
a = corrected direct polarization,
"   b = corrected invert polarization,
t — temperature of solution polarized (20°),
w = weight of sample taken (in this case 10 gm).
Determination of Lactose. — On account of the presence of sucrose in
condensed milk, the lactose cannot be determined directly by polarization.
The copper reduction method is suitable for this purpose, as sucrose does not
reduce Fehling's solution.
Measure 100 cc of the milk solution already prepared into a 250-cc volu-
metric flask and dilute to about 200 cc. Add 6 cc of Fehling's copper sul-
phate solution (see page 158) and make up to the mark. Mix well, filter
through a dry filter and determine lactose as directed on page 212.
Powdered Milk. — The rapid progress made in recent years in
producing a high grade of powdered milk has greatly stimulated
its use by bakers and confectioners. It also is used in ice cream
to give body and smoothness to the product. The spray process
now used in its manufacture probably owes its success to the
comparatively low temperature at which evaporation and con-
densation take place. Milk or evaporated milk is dried by forcing
a fine spray into a current of warm air, thus causing the milk
particles to remain in suspension long enough to lose most of
their water before depositing on the sides of the container.
For the analysis, dissolve 10 gm in water, dilute to 100 cc, mix well and
proceed as outlined for condensed milk. To determine moisture, dry about
2 gm to constant weight at 100° and calculate the per cent loss.
CREAM
Commercial cream must contain not less than 18 per cent of
fat according to the Federal standard. The following table gives
some figures on the composition of a typical milk, cream and