432 



FOODS AND FOOD ADULTERANTS. 



on the same figure with a heavier it is suspended from the hook of the 

 latter. 



FIG. 19. 



For liquids lighter thau distilled water the numbers on the beam 

 may be taken to represent the specific gravity. 



Example. 



Let the 5 g weight be at 9. 

 the .5 g weight be at 1. 

 the .05 g weight be at 4. 

 the .005 g weight be at 5. 



If the beam is in equilibrium at this disposition of the weights and 

 the temperature of the liquid that of the red mark on the bob, the spe- 

 cific giavity would be .9145. The actual weight of liquid displaced 

 would be 4.5725 g, which divided by 5 = .9145. 



Before beginning work with the balance the bob .should be carefully 

 graduated in pure distilled water, recently boiled and at the required 

 temperature. Any variation in the caliber of the bob is thus deter- 

 mined, and any necessary correction can be introduced into the result 

 obtained. 



To change the expression of the specific gravity from direct compari- 

 son with water at any given temperature to the standard of water at 

 15.5 or 4, the factor of the co-efficient of expansion of water must be 

 introduced. One cubic centimeter of water at .'>5 weighs 99. 118 g. 



