IOO 



SPECIFIC GRAVITY, HEAT, 



PART I. 



Atomic Weights, an Atom of Hydrogen being the Unit. 



. 80 

 . 32 



35-5 



39 



85 

 123 

 127 

 204 



In the determination of atomic weights a few cases 

 have occurred of fractional numbers, and although it 

 cannot yet be affirmed that no such cases exist, yet it 

 seems to be established by the new and more perfect 

 analyses of MM. Dumas, Isidore, Williamson, and 

 others, that the atomic weights of substances compared 

 with an atom of hydrogen are in whole numbers. 



This law leads to very important results. For ex- 

 ample, the equivalent weights of the chemical elements 

 of bodies derived from their specific gravities are either 

 identical with, or simple multiples or sub-multiples of, 

 their relative weights. Thus the specific gravity of 

 hydrogen is 0*0693, and that of oxygen is 1*111 ; hence 

 taking hydrogen as the unit of comparison, it is easy to 

 see that 0*0693 : 1*111 : : 1 : 16, the simple multiple of 

 8, the relative atomic weight of oxygen. In fact since 

 each substance has its own specific gravity or weight, 

 that weight must depend upon the weight of its atoms, 

 so that the weights of equal bulks of different sub- 

 stances are proportional to the weights of their atoms, 

 and thus a relation is established between the atomic 

 weights and specific gravities of bodies, so that one 

 being given the other may be found. 



Atoms like their substances have many different 

 capacities for heat and electricity. It was proved by 

 MM. Petit and Dulong, that specific heat, or the 

 quantity of heat required to raise a simple substance to 



