430 FOODS AND FOOD ADULTERANTS 



filled with recently boiled distilled water. The water iii the bath is then 

 brought to the boiling point by means of a lamp and the boiling con- 

 tinued for one half hour. Any evaporation which may take place from 

 the specific-gravity flask is replaced by adding a few drops of boiling 

 distilled water. At the end of the half hour the stopper of the flask is 

 quickly inserted and firmly pressed into its position, any water remain- 

 ing on the top of the stopper being removed by a piece of filter paper. 

 The flask is then removed from the bath, wiped perfectly dry, placed in 

 the balance and weighed as soon as it reaches the temperature of the 

 balance room. The weight of the distilled water which the flask con- 

 tains at the given temperature having been determined, the flask is 

 rinsed with alcohol and ether and dried as in the first instance. It is 

 then tilled with the fat, the specific gravity of which is to be deter- 

 mined, with the same precautions as were used in determining the 

 weight of water.* 



Example of specific gravity of fat, at 100 (boiling distilled water). 



Grams. 



Weight of flask, empty 11.0956 



Weight of flask+water at 100 39. G'JKi 



Weight of water 28.5260 



Weight of flask with fat at 100 36.8691 



Weight of fat 25.7635 



Specific gravity=25.7635-H28.5260=.90316. 



(c) By the Westplial balance. The specific gravity of a fat can be 

 accurately determined by a modification of the balance known as the 

 Westphal. This instrument is show r u in Fig. 18. 



The principle of the apparatus may be briefly stated as follows : A 

 glass bob is so adjusted as to be capable of displacing a given number 

 of graines, five, for instance, of distilled water at a given temperature 

 when wholly immersed in the liquid and suspended by a fine platinum 

 wire. These bobs may be had graduated for any temperature, but most 

 conveniently for those already named, viz, 35 or 40 and 100. It 

 is necessary for accurate work with this instrument that the temper- 

 ature of the fat or oil, the specific gravity of which is to be determined, 

 should be exactly that for which the bob is graduated, as even a slight 

 variation from the prescribed temperature will produce a serious ei for in 

 the result. In order to secure greater accuracy, especially for taking 

 specific gravities at a temperature of 40, a fine analytical balance can be 

 substituted for the Westphal instrument. Such a balance arranged lor 

 use in this way is represented in Fig. 19. It is inconvenient, however, 



* To facilitate the escape of any occluded air in placing the stoppers in the Masks, I 

 have had the stoppers constructed with \\ concave bottom, the center of ,hc concavity 

 being at the opening of the capillary tube. The top of the stopper is also ground to 

 a line I'dgc, so tliat any liquid that may issue from the capillary tube may How away 

 and thus escape uhsorptioq, 



