90 BULLETIN 846 ; U. S. DEPARTMENT OF AGRICULTURE. 



usually requires about 4 hours. It is recommended that weighings 

 be made at the end of 3^ 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. Ex- 

 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 the 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 than 25 inches. Weigh 

 to three decimal places. Express 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. 1 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 con- 

 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 diameter and 350 mm. 



i Zeit. physiol. Chem. (1902), 37: 161. 



