conformity with the Dynamical Theory of Heat and Gases. 255 



more chemical indestructible atoms than that such primary atom 

 is a fraction of a gaseous molecule; but if this feeling can be 

 overcome, the advantage obtained would, I believe, fully repay 

 the effort. To the mathematical student of thermo-molecular 

 physics, there is as distinct evidence of the gaseous molecule of 

 oxygen splitting into two equal parts when combining with hy- 

 drogen to form water, as there is to the astronomer of any of the 

 results of the law of gravitation. When, besides expressing such 

 facts, the vapour-molecule system of exponents is also so much 

 more comprehensive in the information it affords, surely an im- 

 partial and deliberate consideration of the question cannot fail to 

 have its influence. 



I have before me a Table of nearly two hundred gases and 

 vapours whose densities have been experimentally ascertained, all 

 expressed in this way. Each symbol or formula expresses the 

 actual constitution of the gas-molecule in terms of the gas-mole- 

 cules of its constituents, or, in other words, each expresses the 

 constitution of a unit volume of the body in a state of vapour in 

 terms of the unit volume of its constituents ; also the equivalent 

 weight by adding up the value of the symbols. Thus sulphurous 



i 96 



acid, OS 6 = 16+ -^ = 32, which is the vapour-density and also 



the equivalent. Muriatic acid, Cl^H^ = 18 + i = 18|-, which is 

 the vapour- density, but only one-half of the equivalent usually 

 given. 



The mixing up of single and double numbers in tables of 

 equivalents, which still continues in works of authority, seems 

 prejudicial to advancement in theoretical chemistry. For example, 

 if the individuality of the molecule were properly kept in view, 

 alcohol could never have been viewed as the hydrate of oxide of 

 ethyle in a system of notation like that of Gerhardt's, which 

 professes to recognize equal number of atoms in equal volumes, — 

 the fact being that two vapour-molecules of alcohol contain the 

 same elements as one vapour-molecule of ether plus one vapour- 

 molecule of water. If the system recognizes only the simple gases 

 as having the same number of atoms in equal volumes, and the 

 compounds as having varying multiples of these according to 

 what is termed their " rational formula/' then in a cubic foot 

 which contains n number of atoms of oxygen there is %n number 

 of ether-atoms as the greatest number possible ; because if the 

 number were n, each atom of ether would contain half an atom 

 of oxygen (4), which is inadmissible, as an atom applies to the 

 least combining element. In a cubic foot of alcohol vapour, 

 considered as the hydrate of ether, there cannot be more than 

 half the number of atoms that ether has, or \n } for the same 

 reason in respect to the atom of oxygen. On the other hand, if 



