and on the refractive Powers of different Gases, 295 
ments; for its refraction is much weaker than that of this 
liquid. 
The proof of the refracting power of the carbonic acid gas 
was doubly interesting, as a confirmation of the analysis of 
Lavoisier, as well as because carbon enters into the compo- 
sition of a great number of transparent bodies, and consti- 
tutes, according to modern experiments, almost the whole 
body of the diamond, the refractive power of which has been 
remarked by Newton; a result which might be compared 
with that obtained from experiments upon carhonic acid gas. 
Here an anomaly presents itself. The refractive power 
of the carbonic acid gas is a little less than that of the atmo- 
spheric air, and a little greater than that of oxygen. If we 
admit as the most probable chemical constitution of this 
gas that which results from the analysis of Lavoisier, we 
shall ascertain that it is composed of 0°76 in weight of oxy- 
gen and of 0°24 of carbon. It results from this that the re- 
fractive power of carbon is = 1°44; that is to say, less than 
that of water. Every other proportion, into which less ox- 
ygen entered, would give to carbon a refractive power still 
weaker. 
If this result gave rise to doubts upon the proportion ad- 
mitted above, between the two components of carbonic 
acid, we might verify it by this simple method—by exa- 
mining if the refractive power of certain liquid or solid sub- 
stances into which carbon enters in a known proportion, 
with other component parts, of which the relative propor- 
tion and the individual refractive power have been deter- 
mined; by examining, we say, whether the refractive power 
of these really agrees with the results of the calculations 
founded upon the analysis of Lavoisier, which are presumed 
to be exact. 
We have as yet, unfortunately, but a very small number 
of accurate analyses of those substances into which carbon 
enters in a remarkable quantity. These analyses have been: 
made by Lavoisier, Berthollet, Fourcroy, and Vauquelin. 
We have also the observations of Newton upon the refrac- 
tive powers of compounds. 
T4 Thus, 
