THE STANDARD TEMPERATURE. 67 



and making the volumes equal, we have 



*/.:. (2) 



8,- W^pS 



that is, the ratio of the specific gravities of two bodies 

 is equal to that of their densities. 



Now suppose the body whose weight is W^ to be assumed 

 as the standard for specific gravity; then will 8 l be unity, 

 and (2) will become 



W p 



Also, if the same body be assumed as the standard of 

 density, p i will be unity, and (3) will become 



Hence, the measure of the specific gravity of a body 

 is the same as that of its density, i. e., the numbers 8 

 and p are identical, when both specific gravity and 

 density are referred to the same substance as a 

 standard. 



30. The Standard Temperature. The standard sub- 

 stance to which specific gravity and density are referred is 

 not necessarily the same, and therefore S and p will in gen- 

 eral be different numbers. In practice, it is usual to adopt 

 water as the standard in determining the specific gravities 

 of solids and incompressible fluids ; and for the purpose of 

 rendering the comparison more exact, the water must first 

 be deprived by distillation of any impurities which it may 

 contain. 



The dimensions of all bodies being more or less changed 

 by changes of temperature, it becomes necessary to adopt a 

 standard temperature at which experiments for determining 



