APPENDIX. 445 



other solids which are not known in the gaseous form, may 

 be calculated from the density of their compounds with ele- 

 mentary gases of known density. That of carbon, for ex- 

 ample, may be deduced from that of carbonic acid. The 

 calculation involves an assumption as to the equivalent vol- 

 ume of carbon. Assuming it to be the same as that of hy- 

 drogen, the density of carbon vapor is 423 '4. If its equiva- 

 lent volume is the same as that of oxygen or that of hydro- 

 gen, the density is doubled. 



ATOMIC VOLUMES. It is obvious that the number of atoms 

 of a given weight in any mass, must be in proportion to the 

 density of the mass. The size of the same atoms must be 

 less in the same proportion. The atomic volume of any 

 substance is therefore obtained by dividing the atomic 

 weight by the density or specific gravity of the body. The 

 subject of atomic volumes has important relations to the 

 science of crystallography. In comparing atomic volumes 

 it is assumed that the space which a body occupies is com- 

 pletely filled by the atoms, without intervening space. 



ATOMIC HEAT. The numbers 28, 32, 103, represent, in 

 the order in which they are given, the atomic weights of 

 iron, copper, and lead. It is a remarkable fact that if the 

 three metals be taken in these relative proportions, it will 

 require the same expenditure of heat to make them equally 

 hot. 103 pounds pounds of lead can be heated up to 212, 

 for example, by burning the same amount of alcohol which 

 will heat 32 pounds of copper, or 28 Ibs. of iron, to the same 

 degree. Most other metals, and the non-metallic element, 

 sulphur, come into the same class, or in other words, 

 have the same atomic heat. The atomic heat of arse- 

 nic and silver is double that of the elements above men- 

 tioned. Other elements are different in this respect, but 

 commonly by some simple ratio of difference. The cor- 

 respondence is never absolute, but so close as to have lead 



