FEEDS

147

water as otherwise various substances, soluble in water or alcohol
(salts, sugars and amids) would be extracted. Certain other
fat solvents have been used, such as benzol, gasoline and carbon
tetrachloride, but none has been found to be quite as satisfactory
as dry ether.
One form of assembled extraction apparatus is shown in Fig.
41. Any number of separate pieces may be assembled upon one
heater. In Fig. 41 the third extractor is shown in section.
Ether (or other volatile solvent) is placed in the weighed cup a
where it boils and the condensed vapor from, the condenser d
falls to the sample in the porous cup 6. As the solvent fills the
siphon cup c to the level of the siphon bend, the cup automatically
empties into a, below. This process repeats itself indefinitely.
Determination, of Crude Fat.—Wash commercial ether by shaking in a
separatory funnel with two or three successive portions of water and drawing
off and discarding the latter. Add solid sodium or potassium hydroxide
and let stand until most of the water has been abstracted from the ether.
Decant into a dry bottle, add small pieces of cleaned metallic sodium
or sodium wire, freshly extruded from a sodium press, and let stand until
there is no further evolution of hydrogen. Keep the ether, thus dehy-
drated, over metallic sodium in lightly stoppered bottles.
The sample is thoroughly dried at 100° in an alundurn cup or fat-free
paper capsule (or the sample used for the moisture determination is taken),
then placed in an extracting tube and sufficient ether, as above prepared, is
added to the weighed cup a of Fig. 41 (previously cleaned, dried and
weighed) to enable continuous extraction to proceed automatically. The
alundum cup is a porous vessel, cylindrical in shape, and convenient to use
because it is easily cleaned by burning, so that it may be used repeatedly.
It is suitable to use also in fiber filtration, as it permits weighing and burning
of the fiber without removal to another vessel The porous alundum cup,
grade R. A. 98, permits rapid filtering and washing.
Extract the sample for sixteen hours, saving the residue for the fiber
determination (page 148), then remove the cup a and allow the ether to
evaporate, or place the cup in a special apparatus for distilling and recovering
the ether. Dry at 100° for 30 minutes, cool in a desiccator and weigh.
Repeat the drying for 30-minute periods until the weight is constant. From
the difference between the weights before and after extraction, calculate the
per cent of crude fat.
Crude Fiber.—The so-called "crude fiber" is a mixture of
substances which make up the framework of a plant. It is
composed of cellulose, part of the hemi cellulose and lignin of the