70 METHODS OF FIXDIXG SPECIFIC GRA VITY. 



(1) To find the specific gravity of a solid heavier 

 than water. 



Let w = the weight of the solid in air, w' = its weight 

 in water, and S = the specific gravity of the solid, that of 

 water being 1 ; then w w' is the weight lost by the solid, 

 which is also the weight of the water displaced by the solid 

 (Art. 24) ; therefore w and w w' are the weights of equal 

 volumes of the solid and water. Hence we have 



s = -Si. (i) 



W W 



Hence, to find the specific gravity of a solid heavier than 

 water, we have the following rule : Divide its weight by 

 its loss of weight in water. 



(2) To find the specific gravity of a solid lighter 

 than water. 



Since the solid is lighter than water, it will not descend 

 in the water by its own weight ; it must therefore be at- 

 tached to a heavy body of sufficient size and weight to make 

 the two together sink in the water. 



Let w = the weight of the solid in air, 



* = the weight in air of the heavy body 



attached to it, 

 *' = the weight in the water of the heavy 



body, 



w' = the weight in the water of the two 

 together. 



Then w+x w' = the weight of water displaced by the 



two together. 



x x' = the weight of water displaced by the* 

 heavy body. 



Hence, w+x' w' = the weight of water displaced by the 

 solid, and therefore 



