JUNE 20, 1884.] 
in all questions of chemical philosophy, which 
he discussed with great earnestness and warmth. 
There were the same fire and the same exuber- 
ance of fancy which had enchanted me in his 
lectures thirty years before. At an age when 
most men hold speculation in small esteem, I 
was much struck with his criticism of a con- 
temporary, who, he said, had no imagination, 
although he spoke with the highest praise of 
At that time Dumas 
his experimental skill. 
showed no signs 
of impaired 
strength; but 
during the fol- 
lowing year his 
health began to 
fail, and he died 
on the 11th of 
April, at Cannes, 
where he had 
sought a retreat 
from the severity 
of the winter cli- 
mate of Paris. 
Dumas was not 
only eminent as 
an investigator 
of nature, but 
even more eml- 
nent as a teacher 
and an adminis- 
trator. Without 
attempting to de- 
tail Dumas’s nu- 
merous contribu- 
tions to chemical 
knowledge, we 
will here only 
refer to three 
important inves- 
tigations, which 
Bprogneed a 
marked influence 
in the progress 
of chemical sci- 
ence. 
After his removal to Paris he took up the 
problem which the relations of the molecular 
volumes of aeriform substances present; and 
his paper on some points of the atomic theory 
had an important influence in developing our 
modern chemical philosophy. We are sur- 
prised that Dumas did not at once realize the 
consequences which the doctrine of equal 
molecular volumes involves in the interpreta- 
tion of the constitution of chemical compounds, 
and the clear distinction between ‘ the physi- 
cally smallest particles’ and ‘the chemically 
SCIENCE. jal 
smallest particles,’ or the molecules and the 
atoms, as we now call the physical and the 
chemical units. But more than a quarter 
of a century passed before the full harvest of 
this fruitful hypothesis could be reaped. ere 
But if this investigation of gas and vapor 
densities brought a great strain upon the 
dualistic system, the second of the three ‘great 
investigations of Dumas, to which we have 
referred, led to its complete overthrow. The 
most important 
of the  experi- 
mental results 
were the substi- 
tution products 
obtained by the 
action of chlorine 
gas on. acetic 
acid; and the 
capital point 
made, was that 
chlorine could be 
substituted in 
acetic acid for a 
large part of the 
hydrogen  with- 
out destroying 
the acid relations 
of the product; 
and the inference 
was, that the 
qualities of a 
compound = sub- 
stance depend, 
not simply on the 
nature of the ele- 
ments of which it 
consists, but also 
on the manner 
or type according 
to which these 
elements are 
combined. 
To the chem- 
ists of the pres- 
ent day these 
results and inferences seem so natural that it 
is difficult to understand the spirit with which 
they were received forty years ago. But it 
must be remembered that at that time the 
conceptions of chemists were wholly moulded 
in the dualistic system. It was thought that 
chemical action depended upon the antagonism 
between metals and metalloids, bases and acids, 
acid salts and basic salts, and that the qualities 
of the products resulted from the blending of 
such opposite virtues. That chlorine should 
unite with hydrogen was natural, for no two 
