68 



THE STANDARD TEMPERATURE. 



specific gravities must be performed. The English * usually 

 take for this purpose the temperature of 60 Fahrenheit, it 

 being easily obtained at all times, and the tables of specific 

 gravities are usually given with reference to distilled water 

 at this temperature as the standard. When the experiment 

 cannot be performed at the standard temperature, the result 

 obtained must be reduced to what it would be at this tem- 

 perature, i. e., the apparent specific gravity, as obtained by 

 means of water when not at the standard temperature, must 

 be reduced to what it would have been if the water had 

 been at the standard temperature. 



Thus, let p be the density of any solid, S^ its apparent 

 specific gravity as obtained by water when not at the stand- 

 ard temperature, and p t the corresponding density of the 

 water ; and let S be the true specific gravity of the body as 

 determined by water at a standard temperature, the corre- 

 sponding density of the water being p 8 . Then, from (3) of 

 Art 29, we have 



=-, and 

 Pi 



Pt 



(1) 



Calling the density of the standard temperature unity, 

 (1) becomes 



(2) 



That is, the specific gravity of a, body as determined 

 at the standard te?nperature of the water is equal to 

 its specific gravity determined at any other tempera- 

 ture, multiplied by the density of the water at this 

 temperature, the density of the water at the standard 

 temperature being regarded as unity. 



SCH. In the cases that occur most frequently in prac- 

 tice, such nicety is unnecessary, and the experiment may be 



* The French usually take the temperature at which water has its maximum of 

 density, which ia 89 .4 F. 



