236 HISTORY OF CALIFORNIA. 



color and sinking rapidly in water, be fairly assumed 

 to be gold. 



The weight of gold, as of all substances, it is con- 

 venient to estimate relatively, and in comparison with 

 the weight of an equal volume of water. The relative 

 weight, or specific gravity, as it is called, of gold, is 

 remarkably high, the lightest varieties being twelve 

 times heavier than water, and pure gold nineteen 

 times. This is expressed by saying that the specific 

 gravity of native gold is 12 — 19, and the number 

 determined by comparing the weight of the mineral in 

 water and air. 



As the value of gold depends almost entirely on its 

 specific gravity, and this test, therefore, is of the 

 greatest practical importance, it will not be out of 

 place if we here explain some very simple apparatus 

 for the determination of this point. 



If the specimen then is large enough to be sus- 

 pended conveniently by a thread, weigh it first in air 

 by a fine balance, expressing the result in grains, and 

 taking care previously to remove dust or loosely adher- 

 ing particles. Then suspend it by a horsehair from 

 the scale-pan (it is convenient to have a hook attached 

 to it for this purpose,) and thus suspended, immerse 

 it and re-weigh it in water, taking care that it is 

 covered on all sides by at least half an inch of water, 

 and carefully brushing ofi" with a feather any bubbles 

 of air that adhere to the surface. The results may 

 then be noted as follows : — 



Weight of substance in the air in grains .... 



Deduct weight of ditto in water 



Difference . , . 



This result gives the weight of a bulk of water 



