186 FERGUSON'S LECTURES 



vity of silver (found in the table) from that of the com- 

 pound, and the specific gravity of the compound from that 

 of gold ; the first remainder shews the bulk of gold, and 

 the latter the bulk of silver, in the whole compound : 

 and if these 'remainders be multiplied by the respective 

 specific gravities, the products will shew the proportion 

 of weights of each metal in the body. Example. 



Suppose the specific gravity of the compounded body 

 be 13 ; that of standard silver, (by the table) is 10.5, 

 and that of gold 19.63 ; therefore 13.5 from 13 remains 

 2.5, the proportional bulk of the gold ; and 13 from 19.63 

 remains 6.63 the proportional bulk of silver in the com- 

 pound. Then, the first remainder 2.5, multiplied by 

 19.63, the specific gravity of gold, produces 49.075 for 

 the proportional weight of gold ; and the last remainder 

 6.63 multiplied by 10.5, the specific gravity of silver, pro- 

 duces 69.615 for the proportional weight of silver in the 

 whole body. So that for every 49.07 ounces or pounds 

 of gold, there are 69.6 pounds or ounces of silver in the 

 body. 



Hence it is easy to know whether any suspected 

 metal be genuine, or alloyed, or counterfeit ; by finding 

 how much it is heavier than its bulk of water, and com- 

 paring the same with the table : if they agree, the metal 

 is good ; if they differ, it is alloyed or counterfeited. 

 How to A cubical inch of good brandy, rum, or other proof 

 tuouHu' spirit 8 * weighs 235.7 grains ; therefore, if a true inch 

 quors, cube of any metal weighs 235.7 grains less in spirits than 

 in air, it shews the spirits are proof. If it loses less of 

 its aerial weight in spirits, they are above proof ; if it 

 loses more, they are under. For, the better the spirits 

 are, they are the lighter ; and the worse, the heavier. 

 All bodies expand with heat and contract with cold, but 

 some more and some less than others. And therefore 

 the specific gravities of bodies are not precisely the same 

 in summer as in winter. It has been found that a cubic 

 inch of good brandy is 10 grains heavier in winter than in 



