C. Marignac— Chemical Equivalents and Atomic Weights. 95 
among chemists, who accept this system of notation, as to the 
atomic weights, except for a few bodies that are not, as yet, 
sufficiently known; whose physical properties have not been 
sufficiently studied, and for which, besides, the idea of equiva- 
ents is quite as uncertain as that of atomic weights. 
I am perfectly aware that the majority of chemists, who have 
adopted atomic formulas, believe that they are now able to give 
a rigorous definition of atomic weights. Starting from mole- 
cules, which they define as the smallest quantity of a body, 
simple or compound, which can exist in the state of liberty ; 
admitting as an axiom the principle of Avogadro, which states 
the equality of volume of all molecules in a gaseous state, from 
which may be deducted their relative weights, they define the 
atom as the smallest quantity of a body which may enter into 
the composition of a molecule. This definition allows them to 
determine the atomic weights with certainty, at least for those 
bodies that enter into volatile combinations. I have not given 
great weight to this consideration because, not more than 
rthelo 
obtained by considerations based on the physical properties. 
the atomic 
established, nor indeed had their equivalents. This observa- 
tion might be appealed to as the strongest proof of the accuracy 
of the definition of atomic weights, but I have no wish to admit 
it, as constituting a sufficiently sure base for the determination 
of atomic weights. 
I have here to answer an objection, which I acknowledge to be 
Serious, and which I believe is at the bottom of the opposition 
of erthelot. The atomic weights rest on an hypothesis 
which has never been, and, in fact, can never be demonstrated, 
which many scientific men do not consider as verisimilar, that 
of the existence of atoms. in : 
_Tam nearly ready to agree with M. Berthelot in his opposi- 
tion, and I have certainly no idea of defending the atomic 
atomic weights. My answer to the objection stated above is 
that the existence of atoms is only useful in justifying the 
on the indivisibility of atoms; consequently we may consi 
atomic weights as entirely independent of this indivisibility. 
