IN STUDYING QUESTIONS OF CHEMICAL MECHANICS. 341 
more evident which I have just related respecting decrystallized 
cane-sugar, prove therefore that the solid state is by no means in- 
compatible with the exercise of the rotatory power, as very di- 
stinguished philosophers had supposed it to be, against all pro- 
bability, when these phzenomena were first discovered* ; but, as 
I have stated, they may be rendered less sensible, or completely 
masked, by the more energetic phenomena of polarization 
which crystallization developes when it accompanies solidifica- 
tion. For example, I have never been able to observe traces of 
it in the most transparent samples of solid camphor, although 
this same camphor acts with much energy when dissolved in 
alcohol, or liquefied by heat, and brought to the state of ebul- 
lition. But it is likewise easy to demonstrate, on studying the 
action of the solid camphor on polarized or non-polarized light, 
by the modifications which it produces, that the smallest frag- 
ments of this substance, apparently the best-crystallized exter- 
nally, are internally only confused assemblages of an infinity of 
small crystals turned in all directions, so as to constitute veri- 
table macles ; we ought not therefore to be surprised if the proper 
polarizing action which these crystals exercise individually, mask 
the much weaker effects of the rotatory power of the particles 
composing them. 
I have sometimes imagined that I perceived traces of these 
molecular effects on the directions of the axes of the crystallized 
cane-sugar, but I have not been able to procure pieces sufficiently 
large and pure to render this result certain. I have vainly 
attempted also to obtain tartaric acid fused into transparent and 
solid masses, to make with it the same observations. They 
would, moreover, have had another kind of interest; for the 
rotatory power of this acid in its aqueous solutions diminishes 
at an equal temperature, in proportion as the water present is 
* This idea was broached by Sir John Herschel in his ‘ Treatise on Light,’ 
§ 1046, and it has been reproduced without observation in the translation of 
that work published at Paris; I cannot therefore pass it by in silence, coming 
as it does from so distinguished a philosopher. Sir John Herschel objected 
that neither solid camphor nor crystallized cane-sugar, observed in the direction 
of one of its axes, manifested any rotatory power, whilst, on the other hand, 
crystallized quartz, which exercises this power in a solid state, ceases to mani- 
fest it when fused by heat or combined with potash. But the considerations 
which I have now given very well account for these facts. In the solid cam- 
phor, and in the crystallized cane-sugar, the crystalline state developes polarizing 
actions whose energy masks the effects of the rotatory power, by depriving 
them of the light on which they should act. In quartz fused or disaggregated 
by combination with potash, rotatory action is no longer observed, because it 
was not there molecular. It was a result of its lamellar constitution which the 
disaggregation has destroyed. 
VOL. IV. PART XIV. 2B 
