FLOATING BODIES, 193 



at rest, wherever it is placed in the interior of the 

 liquid. 



A body capable of remaining at rest in every position in the 

 interior of a liquid cannot be maintained in this state for any length 

 of time ; for the specific gravity of the body and of the liquid must 

 be exactly equal, hat the specific gravity of bodies is constantly alter- 

 ing in consequent of changes of temperature, and these alterations, 

 though slight, "'are sufficient to cause the body either to sink or to 

 rise in the liquid. A mixture of alcohol and water may be used, as 

 in the case of the drop of oil (fig. 12), for maintaining a solid body 

 suspended within a liquid. If the mixture is not thoroughly stirred, 

 it will contain more water below than near the surface, the lower 

 strata will therefore be heavier, and a piece of stearine-candle will 

 remain at rest when immersed in the liquid. The mixture should 

 contain but little alcohol, for stearic acid, the substance of which 

 these candles are made, is very little lighter than water. If a hen's 

 egg be placed in a saturated solution of common salt in water, it 

 will rise to the surface ; but if pure water be gradually added to the 

 solution, the egg may be made to sink below the surface and may 

 be kept suspended in the interior of the liquid. 



If the specific gravity of a body is less than that of 

 the liquid in which it is immersed, the volume of 

 liquid displaced weighs more than the body ; the ' loss 

 of weight ' exceeds in this case the weight itself, that 

 is, the upward pressure of the liquid predominates over 

 the action of gravity on the body, and the latter rises 

 , to the surface : the body floats. The weight of a float- 

 ing body is exactly borne by the liquid, and as by the 

 principle of Archimedes an immersed body loses a part 

 of its weight equal to the weight of the displaced liquid, 

 it follows that the weight of a floating body is equal to the 

 weight of the displaced volume of liquid. A body which 

 weighs 100 gr , displaces lOCF of water when it floats, 

 that is, 100 CC of the volume of the body is immersed 

 below the surface of the liquid. 



