IN STUDYING QUESTIONS OF CHEMICAL MECHANICS. 343 
of 7°5, and I moreover filled a small test-tube with it. The 
whole was placed in a freezing mixture, composed of crystallized 
chloride of calcium and snow, the temperature of which fell lower 
than 35° below zero. After remaining there sufficiently long, the 
test-tube was withdrawn; then, having ascertained through its 
sides that the matter which it contained still exercised an action 
upon the polarized light, but whose direction and energy were not 
sought to be determined, it was broken with a hammer, and I 
found the inclosed mass broken into fragments perfectly solid, 
similar in appearance to barley-sugar or to solid resin. This being 
ascertained, the rectangular box was withdrawn, and I sought to 
observe through its sides the power which the internal mass which 
had remained transparent exercised. I found it still in the same 
direction as in the semi-fluid state. But it was evidently modi- 
fied by the phznomena of polarization analogous to those which 
annealing produces in glass; and it was unequally so in the 
different portions of its entire mass. As the layer of congealed 
vapour which was deposited incessantly upon the external layers 
of the box destroyed their transparency, and might even have 
interfered with the results, these sides were well-cleaned before 
the observation. Now, after one of these frictions, a kind of 
sudden cracking was heard, which made me think the box was 
broken; but it was only an internal movement of the inclosed 
substance, which immediately became opake and traversed by 
a thousand fissures. 
In proportion as it commenced to reacquire the external tem- 
perature, the transparency reappeared, and with it the rotatory 
power. This restoration took place, as was to be expected, at 
first near the external surfaces, which showed that the central 
mass, still solid, consisted of a kind of nucleus bristled with an 
infinity of very long needles, absolutely similar to those which 
are developed in many substances when they crystallize. The 
same phznomena of sudden cracking, followed by a breaking- 
up and opacity, and then by partial fusion with crystalline struc- 
ture, were again reproduced in a second experiment, in which 
the same kind of turpentine was submitted to a cooling rather 
less intense. M. Regnault suggested to me that it would be 
interesting to profit by the inequality of the fusion to endeavour 
to isolate the portion of the mass which solidifies in the form of 
needles, because, probably, a definite product might thus be ex- 
tracted from it. I merely mention this ingenious idea, however, 
which other experimentalists will be better able to realize. 
2B2 
