44 Experimental Philosophy. [Lecture 4. 



that sinks displaces a quantity of water exactly 

 equal to its own bulk, it follows, that every body 

 when immersed in water loses so much of its 

 weight as is equal to the weight of an equal bulk 

 of water. Thus, if the body, when weighed in 

 air, is two ounces in weight, and an equal bulk of 

 water is one ounce, it will of course lose, when 

 weighed in water, one ounce of its apparent 

 weight. It is by this means .that adulterated 

 metals or coins are distinguished from the true 

 ones : thus copper is bulk for bulk heavier than 

 tin, and gold is heavier than copper or brass, 

 which last is a mixture of copper and zinc. If 

 therefore a brass counter is offered for a guinea, if 

 of the same weight, though it may not to the eye 

 appear much larger than a real guinea, yet you 

 may depend upon it that it is so in fact. We will 

 then take a guinea, which we are sure is real 

 gold, and weighing it first in air, and then in 

 water, we shall find it loses about one-nineteenth 

 of its weight in the latter. We then weigh the 

 brass counter in the same way, and find it loses 

 about one-eighth, which we find is much more, 

 and therefore we cannot doubt but the coin is 

 made of base metal. When we look at tables of 

 specific gravities, we see the specific gravity of 

 gold put down at about nineteen one-half, of 

 mercury at about thirteen one-half, lead eleven 

 one-quarter, silver ten one-quarter, copper eight 

 one-half, iron seven one-half, tin seven one- 

 quarter, &c. ; that is, gold is nineteen times one- 



