218

QUANTITATIVE AGRICULTURAL ANALYSIS

Determination of Total Solids.—Use 10 cc of the solution just prepared
and dry as directed on page 204, drying on either sand or asbestos fiber.

Determination of Ash.—Evaporate 10 cc of the solution to dryness in a
platinum or porcelain dish on the water bath and ignite the residue as directed
on page 204.

Determination of Protein.—Determine the nitrogen in 10 cc of the
solution using the Kjeldahl method as described on page 151 and multiply
by 6.38 to obtain the equivalent of protein.

Determination of Fat.—Weigh 4 to 5 gm of the homogeneous sample into
a Eohrig tube or similar apparatus, dilute with water to about 10.5 cc and
proceed as directed on page 205.

Determination of Sucrose in Sweetened Condensed Milk.—Prepare a
reagent for clarification as follows:

To 220 gm of yellow mercuric oxide add 400 cc of water and sufficient
concentrated nitric acid to form a clear solution, being careful to avoid an
excess. Dilute to about 900 cc and add sodium hydroxide solution, slowly
and with constant shaking, until a slight permanent precipitate is obtained.
Dilute to 1000 cc and filter. The solution will become acid in time, due to
hydrolysis and precipitation of basic mercuric nitrate. Dilute base solution
may be added to correct this.

Introduce 50 cc of the milk solution already prepared into a 100-cc
volumetric flask, add 25 cc of water, mix, add 5 cc of mercuric nitrate solu-
tion arid shake. Without delay, and while stirring constantly, add enough
of a 2-per cent sodium hydroxide solution to render the solution neutral to
litmus paper, being careful to avoid a basic reaction. Dilute to the mark on
the flask, mix thoroughly and filter through a dry paper, discarding the
first 10 cc of filtrate.

Polarize the filtrate in a 200-mm tube at 20°, then invert as follows:
Pipette 50 cc of the filtrate into a 100-cc volumetric flask and add 5 cc of
concentrated hydrochloric acid, slowly and mixing well. Set the flask
aside for 24 hours at a temperature of 20° to 25°. Polarize the solution of
invert sugar in a 200-mm tube at 20° and multiply the reading by two, to
correct for the dilution.

Correct both direct and invert readings for the volumes occupied by the
precipitated protein and fat at the time dilution was made, using the per
cents of these substances as already determined and assuming a volume of
0.8 cc and 1.075 cc, for 1 gm of protein and fat, respectively. The volumes
of these substances will be:

„ _10(0.8P + 1.075F)

3^1^12 = o.08 P + 0.1075F,

100
and the corrected readings on the saccharimeter:

/100 - V
\ 100

where

V = volume, of protein and fat precipitate,
P = per cent of protein,

R

/100-0.08P-0.1075F\

I __ _____________I rp

\ 100 r

(2)