216 Testing Milk and Its Products. 



248. a. Specific gravity is determined by means of 

 a picnometer cr specific-gravity bottle, since more ac- 

 curate results will thus be reached than by using an or- 

 dinary Quevenne lactometer. A thermometer is ground 

 into the neck of the specific-gravity bottle so as to form 

 a stopper, and the bottle is provided with a glass-stop- 

 pered side-tube, to furnish an exit for the liquid on ex- 

 panding. A specific-gravity bottle holding 100 grams 

 of water is preferably used. The empty and scrupu- 

 lously cleaned bottle is first weighed on a chemical bal- 

 ance. The bottle is then filled with recently-boiled dis- 

 tilled water of a temperature below 60 F. (15.5 C.) ; 

 the thermometer is inserted, and the bottle is warmed 

 slightly by immersing it for a moment in tepid water 

 and left standing until the thermometer shows 60 F. ; 

 the opening of the side tube is then wiped off and closed 

 with the stopper, and the water on the outside of the 

 bottle and in the groove between its neck and the ther- 

 mometer is wiped off with filter paper or a clean hand- 

 kerchief, when the bottle is again weighed. The weight 

 being recorded, the bottle is emptied and dried in a 

 water oven, or if sufficient milk is at hand, the bottle is 

 repeatedly rinsed with the milk, the specific gravity of 

 which is to be determined. It is then filled with milk 

 in a vsimilar manner as in case of water ; the tempera- 

 ture of the milk should be slightly below 60 F. and is 

 slowly brought up to this degree after the bottle has 

 been filled, proceeding in the same way as before with 

 water ; the weight of the bottle and milk is then taken. 



The weights of water and of milk contained in the 

 specific-gravity bottle are found by subtracting the 



