chap, xix.j SPECIFIC GRAVITY. 199 



to which the body is suspended, place a vessel with 

 water, and allow the body to hang in the water. The 

 body will displace its own volume of water, and will 

 be pressed upwards by the weight of that amount of 

 water. The body will, therefore, lose weight to this 

 extent. By the balance the weight of the body in 

 water is now estimated, and it will be equal to the 

 weight of the body in air, less the weight of a quantity 

 of water equal to its own volume. Thus, we have the 

 weight of the body in air, and we have the weight of 

 an equal volume of water, the loss of weight, namely, 

 experienced by the body, and the relation of these two 

 gives the specific gravity. Thus : 



Weight in air 



. , , . . , . . = specific gravity : 



weight in air weight in water 



{ weight of equal volume 

 of water) 



or, to put it in symbols, 



^ = sp- gr * 



This method, it is observed, is applicable only to solid 

 bodies not soluble in water. 



It is worthy of remark that if French weights 

 are employed (grammes) the process that has been 

 performed indicates not only the specific gravity of the 

 body, but also its volume. Since one cubic centi- 

 metre of water, at standard temperature, weighs one 

 gramme, if the solid body weighed in water is found 

 to displace ten grammes of water, that means its 

 volume is equal to ten cubic centimetres. 



Precisely the same method is applicable to liquids. 

 From the pan of a balance is suspended a solid body, 

 not attacked by water or the liquid to be examined, 

 and its weight is accurately counterbalanced. The 

 body is now allowed to hang in water, and it being 

 pressed upward by the volume of water it displaces, 



