Evaporate 500 cc. of the sample in a porcelain evaporating dish to a
volume of about 50 cc. By means of a rubber-tipped glass rod remove to
the bottom of the dish the solid matter attached to the sides, and add
normal sulfuric acid to neutralize the alkalinity. Do not use an excess
of acid. Then evaporate the contents of the dish to dryness. Treat the
dry residue with boiling ether, rubbing the bottom and sides of the dish
to insure complete solution of fat. Three extractions with ether are
required. Filter the ether solution through a 5 cm. filter into a
weighed flask having a wide mouth. Evaporate the ether slowly, and dry
the flask at 100° C. for 30 minutes. The increase in weight of the flask
gives the amount of fats, or, in more precise language, the
ether-soluble matter.
An excess of acid gives too high results because of the formation of
fatty-acid residues.