190 DETERMINATION OF SPECIFIC GRAVITIES. 



the shorter pan of the balance until it is in equilibrium 

 with the longer; the body is then suspended to the shorter 

 pan by a piece of thread so that it can be immersed in 

 water. Let the body, for instance, be the glass stopper 

 of a bottle; if its weight in air is 46 gr , and its weight in 



46 46 



water 26 8r ,its specific gravity is = = 2 -3. 



4b 2 b 20 



The volume of bodies which have an irregular shape 

 may be determined by the same principle. For a body 

 immersed in water loses one gramme of its weight for 

 every cubic centimetre of its volume ; hence, conversely, 

 the volume of the body contains as many cubic centi- 

 metres as there are grammes in the weight lost by it 

 when it is immersed in water. The glass stopper lost 

 20 grammes; hence its volume is 20 cubic centimetres. 



The loss of weight of a body which floats upon 

 water can only be ascertained by tying to it another 

 body which sinks and causes the first body to be com$ 

 pletely immersed. For example, the specific gravity 

 of a piece of cork which weighs 4 gr , may be found by 

 tying to it a piece of lead. If the latter weighs 

 both together weigh 27 gr ; and suppose we find theii 

 weight, when together in water, to be 9 gr ; if the 

 alone weighed in water 21 gr , the loss of both togethei 

 viz., 27 9 = 18 s1 , diminished by the loss of the lea 

 alone, viz. 23 21 = 2 gr , gives the loss of the coi 



alone, viz. 18 2 = 16 gr . The specific gravity of th< 



4 

 cork alone is therefore = 0'25. 



16 



The specific gravity of a liquid body may be als< 

 determined by the principle of Archimedes, for it 

 only necessary to weigh the same solid body succei- 



