Specific Gravities. 311 



Another method is to determine the specific gravity of the 

 body with reference to some liquid, as alcohol or oil, in which 

 no solution takes place, and whose specific gravity, compared 

 with water is known. We have then simply to use the propor- 

 tion, as the specific gravity of water, is to that of the fluid used 

 so is the result above found to the result sought. 



429. If the same body be immersed in another fluid, whose 

 specific gravity is denoted by S", and w' represent the weight 

 necessary to counterbalance it ; as in the former case we had 

 w = Sb S' 6, we shall have, in like manner, w' = Sb 5" b. 

 Now these two equations give 



= Sb w and S" b S b 



whence, dividing this last by the preceding, we obtain 



#~ " " Sb TO* 



Knowing, therefore, the absolute weight Sb of a body, and its 

 weight w' in a fluid, and its weight w in any other fluid, we easily 



determine the ratio -^ of the specific gravities of these two 



fluids. 



By taking a solid glass ball and grinding it to such a size 

 that it shall lose just a thousand grains, for instance, when weigh- 

 ed in distilled water, at the assumed temperature, then by observ- 

 ing the loss of weight / in grains, sustained on being weighed 

 in any other fluid, we shall have 



1000 : / :: 1 : 5 = 



1000 



Thus the specific gravity of the fluid in question is obtained 

 by dividing / by 1000, or removing the decimal point three 

 places to the left. If a larger number of decimal places were 

 required, we should employ a ball weighing 10000 or 100000 

 grains, and divide accordingly. 



430. The precious metals being heavier than those of less 

 value, when they are debased, it must be by means of some sub- 

 stance of less specific gravity, and the compound will conse- 

 quently be lighter than the metal it is intended to represent. 



