DAIRY

and 2 cc of water, wash the solution through with hot water

and determine copper by any of the methods In Łet\i

analysis? described on pages 159 to 16:1

Optical Methods.—The ability of carbohydrates

containing one or more asymmetric atoms to

rotate the plane of polarization of polarized
affords the basis for an Important method for
determination. The proteins of milk are slightly
optically active, hence they must be removed before
^se can be determined.

subject of polarimetry Is discussed on 121

to 137, Part II. This should be reread before starting
the determination of lactose. The instrument de-
signed especially for sugar determinations is called a
saccharimeter. Its graduations read directly in per
cent of sugar when a definite specified weight ft he
"normal weight)" Is contained In 100 cc when

the polarization Is made in a 200-min tube. The
following determination is based upon the use of an
instrument bearing the International scale. (See
page 130, et seq.)

^Protein Precipitation.—By treatment of milk with
a^n acid solution of mercuric Iodide the proteins are
combined with the mercury and flocculation results.
If the solution is then diluted to a definite volume
without previous filtration the solids present cause a
volume error unless a correction is applied. It has
boon, found that a close approximation may be made
"by deducting 2.6 cc for the volume of precipitate
obtained from, the sample as specified below, the
dilution being accomplished in a flask graduated
to contain 102.6 cc. If a flask graduated in this
manner Is not at hand, prepare one as follows:
Fill a 100-cc volumetric flask exactly to the mark
with distilled water. From a burette add 2.6 cc
more and mark the position of the bottom of the
meniscus with a strip of label. Mark permanently,
if desired, by the method described on 45,

Part I.

SSStt

y

m. 49.-

determina-
tion.