96 @. Marignac—Chemical Equivalents and Atomic Weights. 
In reality, I consider atomic weights, and I believe that many 
chemists agree in this, as being only equivalents, in the deter- 
mination of which arbitrary Sidi ventions have been replaced 
by scientific considerations, based on the study of physical 
properties. 
et us now sum up the advantages that atomic notations 
same e divergence exists for equivalents. 
Atomic weights are exactly nes Shee to the specific pi 
of simple gases, that are not liquifiable, which agreement 
not exist for equivalents. According to the law of Dulong atid 
Petit, the specific heats of the atoms of all simple bodies, either ' 
solid or liquid, are nearly the same, except for three bodies, 
carbon, boron and silicon, whose ‘physical properties offer 
Equivalents do not offer this concordance. I will not insist on 
the objection raised by M. Berthelot, and founded on this, that 
the equality of specific heats of atoms is far from being absolute, 
as he was sufficiently answered b . Wiirtz and Fizeau. I 
will merely add that if we only admitted physical laws that are 
absolute, we should have to reject them all. Even the law of 
volumes of Gay Lussac would have to be dropped, as it has 
been ascertained that all gases have not the same coéfficient of 
expansion, so that the existence of simple ratios in combina- 
tions by volume are not strictly accurate. 
As to compound bodies, the molecular formulas, based on 
the use of seis weights, present the same advantages, perhaps 
to a ghee degree, when we compare them to the formulas in 
equiv: 
Phe ito use of atomic weights allows us to simplify the formulas 
of a great number of co mpounds by dividing them by two. 
Particularly is this the « case with organic compounds. Not 
only does the formula become simpler, but there is an impor- 
tant advantage gained, that the formulas of almost all com- 
ands correspond to the same volume, which is double the 
volume of the simple atom. The only exceptions are for a 
very limited number of bodies, generally belonging to types of 
complex wed i such as salts of ammonia and of bases 
derived from ammonia; even for these it has not been proved 
that they a not regulated by any law, even if M. Deville is 
