222 Testing Milk and Its Products. 



tinue the extraction for 8 hours. The ether is then re- 

 covered by distillation, and the flasks dried in a steam 

 oven until constant weight; after cooling they are 

 weighed and the amount of fat contained in the quan- 

 tity of milk originally weighed into the tubes is thus 

 ascertained, and the per cent, present in the milk cal- 

 culated. 



Example: Weight of flask -f fat 15.8039 grams. 



Weight of flask 15.5171 grams. 



Weight of fat 2868 gram. 



Milk weighed out 5.1232 grams. 



Per cent, of fat in miIk= -^^°^^'"" =5.60 per cent. 



5.1232 ^ 



254. The Gottlieb method for the determination 



of fat.^ 10 cc. of milk are measured into a glass cyl- 

 inder, % inch in diameter and about 14 inches long (a 

 100 cc. burette or a Eudiometer tube will do) ; 1 ec. 

 cone, ammonia is added and mixed thoroughly with the 

 milk; the following chemicals are next added in the 

 order given: 10 cc. of 92 per cent, alcohol, 25 cc. of 

 washed ether, and 25 cc. petroleum ether (boiling pt., 

 below 80° C), the cylinder being closed with a moist- 

 ened cork stopper and the contents shaken several times 

 after the addition of each chemical. The cylinder is then 

 left standing for six hours or more. The clear fat solution 

 is next pipetted off into a small weighed flask, by means 

 of a siphon drawn to a fine point (see fig. 6, loc. cit.), 

 which is lowered into the fat solution to within % cm. 

 of the turbid bottom layer. After evaporating the ether 

 solution in a hood, the flasks are dried in a steam oven 



1 Landw. Vers. Sta., 40 (1802), pp. 1-27. The metliod is also spoken of 

 as the RSse-Gottlieb method. 



