C. Marignac—Chemical Equivalents and Atomic Weights. 97 
right in thinking that the irregularities they present are not due 
to the decomposition of their vapors. On the other hand, the 
formulas by equivalents teach us nothing on the vapor densi- 
ties of compound bodies, as their equivalents may correspond 
to two, four or eight volumes of vapor, perhaps even of six, i 
the old equivalent of silicon is kept, as is done by many of 
those who prefer the notations by equivalents. Molecular 
formulas also agree with the specific heats of compound bodies 
in the solid state. According to the law of Woestyn, molecu- 
lar heats are proportional to the number of atoms contained 
in the molecule, which law has the same degree of approxima- 
tion as that of Dulong and Petit. Formulas by equivalents do 
not show these properties. : 
Finally, the system of notation, based on atomic weights, 
gives the explanation of several cases of isomorphism which 
are incomprehensible with the notation based on equivalents. 
For instance, in the case of perchlorates and permanganates, 
and in the case of chloride and sulphide of silver when com- 
pared to protochloride and protosulphide of copper. | I may 
also recall that it was by considerations of the same kind that 
I was led to discover oxygen in fluorine compounds of niobium, 
where its presence had not been suspected, and that the formu- 
las of these compounds, expressed in equivalents, would never 
have suggested this idea. 
n presence of these advantages, we may as hat are 
those that are offered by the system of equivalents and its 
seven, which would have given it the same volume as oxygen, 
or 14 which would have accounted for its value of combination 
toward hydrogen and the metals, we may readily believe that 
there will never be a sufficient motive to replace it by one of 
these numbers. The determination of equivalents not being 
governed by any fixed rule, they will not be necessarily modi- 
ed when we come to have a more accurate knowledge of the 
properties of bodies. : : 
In the second place, as, in their determination, no account 1s 
taken of the physical properties of bodies, greater attention can 
given to their chemical equivalence, when it exists. This 
presents some advantages in practical chemistry. : 
These considerations are doubtless of some value; but if we 
examine things a little closer, we may easily see that, in this 
i there is really very little difference between the two 
stems. 
Am. Jour. Sct.—Turrp Serres, Vou. XV, No. 86.—Fss., 1878. 
7 
