344 BIOT ON THE EMPLOYMENT OF POLARIZED LIGHT. 
In the second experiment I submitted to the same test of 
cooling another variety of turpentine, which also exercised the — 
deviation towards the right in its primitive state, but with a less — 
energy than the preceding one. It attained also with much 
greater difficulty complete fusion when heated to the same de- 
gree; and both by this want of relative mobility and by its own 
nature, it appeared to conduct heat much worse. This variety 
did not present any of the phenomena of sudden solidification 
which I have just described. I do not even think that the mass 
ever became solid in the interior; for, on uncorking the flask in 
which it was contained, and trying the state of its surface with — 
a cold metallic point, I found it to have the appearance of a solid 
crust which might be scratched and reduced to powder; but on 
pressing it, the mass yielded, as if it had been preserved from 
cooling and solidification by this external envelope. It is per- 
haps by a consequence of the same fact, that the deviation 
effected by the total mass appeared sensibly the same as previ- 
ous to its being placed in the freezing mixture. 
I availed myself of the same occasion to study the effect of | 
cooling on some other substances. Some very thick syrup of — 
dextrine, submitted to a temperature which was certainly below 
—35°, in a very small flask, preserved its gummy state without 
solidifying, Another more aqueous sample froze completely, 
and became of a dull white, like snow; but after spontaneous — 
melting, it had lost none of its power. A syrup of cane-sugar, — 
acted on by hydrochloric acid, and then neutralized with perfectly 
pure marble, solidified easily. After resuming its liquid state, } 
it exercised the deviation towards the left, as previously. How- — 
ever, according to a remark made by M. Soubeiran, the accuracy } 
of which I have confirmed, when this same altered sugar solidi- 
fies by crystallization, it acquires a rotatory power toward the 
right, as I observed in grape-sugar; and from that time the 
liquefaction in water, even united with the most energetic acids, 
no longer deprives it of this direction. Thus the act of solidifi- 
cation alone did not suffice to modify the altered sugar, as its © 
spontaneous crystallization would have done. It would be inter- 9 
esting to ascertain if this difference in the results is peculiar to 
it, or if it be due to the presence of the chloride of calcium with 
which it was associated. 
[To be continued. ] 
