C. Marignac—Chemical Equivalents and Atomic Weights. 98 
theory, by taking for their weights the sum of the equivalents 
of the elements which they contain. 
I believe I am not in error when I affirm this, as M. Ber- 
thelot* says: ‘One equivalent of phosphoric acid corresponds 
to three equivalents of nitric acid, when it forms a tribasic 
phosphate. 
2. Equivalents are chosen in such a way that compounds, 
which offer the greatest analogies, are represented by similar 
formulas. This principle served as a guide in determining the 
equivalents of aluminum and of copper. It is often in contra- 
diction with the preceding. For instance, aluminum and mag- 
nesium, which are both powerful deoxidizing agents, do not 
replace each other in the proportions indicated by the equiva- 
lents adopted for these two metals. 
| When neither of these rules is applicable, or when the 
lead to complicated formulas, the equivalent of a body is chosen 
in such a way as to give the simplest possible formulas for its 
most important combinations. This rule justifies the adoption 
of the equivalents of nitrogen, phosphorous, arsenic and of some 
other elements, 
e may see by the above that the equivalents constitute a 
purely conventional and arbitrary system, without any scien- 
tific value. 
The explanation I have given of equivalents is somewhat 
different from that which my illustrious teacher, M. Dumas, gave 
in his lessons of chemical philosophy. This eminent chem- 
ist took as his starting point the equivalents of bases, as deter- 
mined by their true chemical equivalence, founded on the same 
quantity of oxygen contained in the base. The equivalents of 
acids are rigorously deducted from the weights necessary to 
neutralize an equivalent of base. Afterwards, he seeks to es- 
tablish the equivalents of the elements by considerations which, 
he acknowledges, are often arbitrary. This method of deter- 
mining equivalents however, has been either never adopted, or 
entirely abandoned, doubtless because it led to formulas which 
are inadmissible. I have given the meaning of equivalents, 
such as they have been adopted, and not such as they might 
have been. 
* Meeting of the Académie des Sciences of June 4th, 1877. I cannot in any 
manner accept what he says, in the same place, that this equivalent of phosphoric 
pendrin to one equivalent of nitric acid in sic phosphates, or two 
€quivalents in bibasic phosphates, To admit such expressions, we must deny to 
Ae nitred serte that all chemists attribute to it in these salts, since the publication 
°f Graham’s researches. 
