IN STUDYING QUESTIONS OF CHEMICAL MECHANICS. 387 
Conclusions. 
70. In the first section of this memoir I have established, by 
reasoning and by experiment, the characters of the action which 
the molecules of a great number of substances exercise upon po- 
larized light; and I have deduced from them formule which 
express all the optical effects which substances thus constituted 
should produce, on a polarized ray traversing sensible thick- 
nesses of them, when they are either in a complete state of dis- 
aggregation, or in a confused state of aggregation, which permits 
the action of their molecules to be freely manifested. I have 
then explained the processes by which these molecular phz- 
nomena are distinguished from similar appearances, which may 
be produced by special circumstances of aggregation, such as 
takes place in regularly crystallized quartz, when the light tra- 
verses it in the direction of its axis of double refraction. It is 
to be remarked that, hitherto, the molecular action in question 
has been observed only in substances, or in combinations con- 
taining at least one organic element. 
71. In the second section I have confirmed these considera- 
tions by a class of facts of a wholly different nature. I have 
shown that, when substances possessing a molecular rotatory 
power are mixed or combined in the liquid state with inactive 
bodies, the resultants of action exercised upon polarized light by 
these mixed systems, in the one or other state, are exactly in ac- 
cordance with the relations of variation observed between their 
densities and those of the primitive systems from which they are 
derived, the comparison being made at one and the same tem- 
perature ; so that the same consequences are deduced as to the 
actual state of combination or non-combination of the systems 
thus formed. ’ 
72. In the third section I have applied these principles to the 
optical effects produced on polarized light by the aqueous solu- 
tions of tartaric acid, of various strengths, either observed pure 
or associated with other substances in the liquid state, and I 
have established the numerical laws to which the succession of 
these phenomena is subjected. In pure aqueous solutions, I 
haye proved that the acid is not merely mixed with the water, 
but that it forms with the entire mass of that liquid presented 
to it a uniform combination, in proportions continually varia- 
ble with the strength, so that the action thus exerted by each 
