DETERMINATION OF SPECIFIC GEAVITIHS. 191 



lively in air, in water, and in the liquid whose specific 

 gravity is to be found. The loss of weight of the body 

 in water gives the weight of a volume of water equal 

 to that of the solid body ; the loss in the liquid gives 

 the weight of an equal volume of the liquid; and con- 

 sequently it is only necessary to divide the second by 

 the first, in order to obtain the specific gravity re- 

 quired. For example, let the glass stopper, which was 

 used before, weigh in air 46 gr , in water 26 gr , and in 

 alcohol 30 gr . This shows that a volume of alcohol equal 

 to that of the stopper weighs 46 30 = 16 gr , while an 

 equal volume of water weighs 46 26 = 20 gr : the spe- 



1 R 



cific gravity of the alcohol is therefore = 0*8. 



The weight lost by a body immersed in a liquid does 

 not disappear altogether. If the body is immersed in 

 a vessel with a lateral spout, as in fig. 136, the dis- 

 placed water leaves the vessel, and the pressure upon 

 the base is not altered ; nevertheless the pressure due 

 to the weight of the displaced water is now exerted 

 upon the base of the vessel into which the water has 

 been discharged. Again, if the water cannot escape, it 

 will rise in the vessel when the body is immersed, and 

 the pressure upon the base of the vessel will increase: 

 the vessel will appear heavier than before, and if it 

 were placed in the scale-pan of a balance and in equili- 

 brium, the increased pressure would cause the scale- 

 pnn to descend when a body is immersed in the liquid 

 as shown in fig. 137. 



21. Floating Bodies. Hydrometers. When a body 

 which is not much heavier than water (or which has a 

 specific gravity not much greater than unity) is im- 





