Specific Gravities. 319 



435. According to what is above laid down, the specific 4 ^ J - 

 gravity of a body multiplied by its bulk gives its weight. Now 



the density multiplied by the bulk gives what is called the mass 

 of the body, which is proportional to its weight. Hence the 

 specific gravity multiplied by the bulk, is proportional to the 

 density multiplied by the bulk; therefore the specific gravities of 

 bodies are proportional to their densities. Thus 5, S 7 , being the 

 specific gravities, w, a/, the weights, 6, 6 X , the bulks, A, A 7 , the 

 densities, and m, w 7 , the masses of two bodies, 



Sb = w, and Sty = a/; 

 also, 



A b = m : A' b' =. m' : : w : a/ ; 

 whence 



A 6 : A' b' : : S b : S 7 6 7 , 

 or, 



A : A 7 : : 5 : S 7 . 



By employing the same unit in both cases, as water, for ex- 

 ample, at the same temperature, the specific gravities would be 

 equal to the densities. 



436. If fluids of various densities, and not disposed to unite by 

 any chemical affinity, be poured into a vessel, they will arrange 

 themselves in horizontal strata, according to their respective 

 densities, the heavier always occupying the lower place. This 

 stratified arrangement of the several fluids will succeed, even 

 though a mutual attraction should subsist, provided only that its 

 operation be feeble and slow. Thus, a body of quicksilver may 

 be at the bottom of a glass vessel, above it a layer of concen- 

 trated sulphuric acid, next this a layer of pure water, and then 

 another layer of alcohol. The sulphuric acid would scarcely 

 act at all upon the mercury, and a considerable time would 

 elapse before the water sensibly penetrated the acid, or the al- 

 cohol the water. Bodies of different densities might remain 

 suspended in these strata. Thus, while a ball of platina would 

 lie at the bottom of the quicksilver, an iron ball would float on 

 its surface ; but a ball of brick would be lifted up to the acid 

 and a ball of beech would swim in the water, and another of 

 cork might rest on the top of the alcohoK 



