90 BULLETIN 846, U. S. DEPARTMENT OF AGRICULTURE. 
usually requires about 4 hours. It is recommended that weighings 
be made at the end of 34 hours of drying, and thereafter at intervals 
of about 30 minutes. Weigh to three decimal places. There is an 
appreciable gain in weight after the minimum has been reached. Hx- 
press the results as per cent on the wet basis. 
ETHER EXTRACT. 
Extract the dry residue from the determination of solids with abso- 
lute ether, preferably in a Knorr apparatus, but if this is not available, 
in a Johnson extractor. Cut through the sides of the lead dish con- 
taining the solids at four equidistant points. Place the dish upon a 
fat-free filter paper. Flatten down the sides of the dish. Place 
another fat-free filter paper on top of the flattened dish, and roll the 
papers and dish into a cylinder which will fit the extraction tube fairly 
snugly. In making the cylinder, turn in thé ends in such a way as to 
prevent solid particles from dropping into the extraction flask. 
Place the cylinder in the extraction tube without any asbestos plug 
below it. If the extractor is working rapidly, three hours is sufficient 
to insure a proper extraction. 
Distill off the ether from the extraction flask, and dry the extract for 
one hour at 55° C., in a vacuum of not less aan 25 inches. Weigh 
to three decimal places. Kixpress the results as per cent on the wet 
basis. 
The ether used should not contain any alcohol or water, as a higher 
result is obtained when either is present. It is, therefore, understood 
that ether freshly distilled from sodium will be used. 
ACIDITY OF THE FAT. 
Dissolve the fat obtained in the determination of ether extract in 
50 cc. of neutral benzol to which has been added 2 drops of phe- 
nolphthalein indicator. Titrate with N/20 sodium ethylate. Ex- 
press the results as the number of cubic centimeters of N/20 sodium 
ethylate required to neutralize 1 gram of fat. 
AMMONIA NITROGEN. 
The titration method is an adaptation of Folin’s method for the de- 
termination of ammonia in urine.’ It consists essentially in making 
the sample alkaline, removing the liberated ammonia by aeration, 
and catching it in a measured quantity of standardized acid, The 
excess acid is then titrated. 
The apparatus consists of the following: (1) A wash bottle cen- 
taining dilute sulphuric acid (about 35 per cent) to remove any am- 
monia that may be present in the air entering the system. (2) Some 
form of trap to prevent sulphuric acid being carried over mechanically. 
(3) An aerating cylinder about 50 mm. in Ss and 350 mm. 
1 Zeit. reel Grom (1902), Sts L6L. 
