1414 FOODS AND FOOD ADULTERANTS. 



The flask is filled with freshly boiled and still hot distilled water and 

 placed in a bath of distilled water. The water of the bath is kept in 

 brisk ebullition for thirty minutes, any evaporation from the flask 

 being replaced by the addition of boiling distilled water. The stop- 

 per, previously heated to 100, is then inserted, the flask removed, 

 wiped dry, and after it has nearty cooled to room temperature placed 

 in the balance, and weighed when balance temperature is reached. 



Second method.* The following formula may be used for calculating 

 the weight of water ( W T ) which a given flask will hold at T (weighed 

 in air with brass weights at the temperature of the room) from the 

 weight of water (W*) (weighed in air with brass weights at the tem- 

 perature of the room) contained therein at t: 



d^ 



w*= w tc [i + r (T 0] 

 d i 



d? = the density of water at T. 



d i =the density of water at t. 



;K = the coefficient of cubical expansion of glass. b 



DETERMINATION. 



Weight of fat at the temperature of foiling water. The flask is 

 rinsed with alcohol and ether, and dried for a few minutes at the tem- 

 perature of boiling water. It is filled with the dry, hot, fresh -filtered 

 fat, which should be entirely free from air bubbles, replaced in the 

 water bath, and kept for thirty minutes at the temperature of boiling 

 water. The stopper, previously heated to 100, is inserted, the flask 

 removed, wiped dry, placed in the balance after it has nearly cooled 

 to room temperature, and weighed when the balance temperature is 

 reached. The weight of fat having been determined, the specific 

 gravity is obtained by dividing it by the weight of water previously 

 found. 



Example : Grams. 



Weight of flask, dry 10. 0197 



Weight of flask, plus water 37. 3412 



Weight of water 27. 3215 



Weight of flask, plus fat 34.6111 



Weight of fat .., 24.5914 



Specific gravity = 24.5914 -^ 27.3215 = 0.90008. 



The weight of the flask dry and empty may be used constantly if 

 great care be taken in handling and cleaning the apparatus. 



Example: Grams. 



Weight of flask, dry and empty 10. 0028 



Weight of flask after three weeks' use 10. 0030 



a E. E. Ewell, U. S. Dept. Agr., Div. Chem. Bui. 62, p. 125. 



b This factor is commonly given as 0.000026, but it varies considerably. Schulze 

 (Ztschr. anal. Chem., 1882, 21, 167-177) found the glass used by him varied from 

 0.0000288 to 0.0000305; an average of these is 0.0000296. Ewell has used 0.000028 in 

 his work, U. S. Dept. Agr., Div. Chem. Bui. 62, p. 121. 



