EVOLUTION OF LIGHT DURING CRYSTALLIZATION. 157 
ART. XXIII. — ON THE EVOLUTION OF LIGHT DURING 
CRYSTALLIZATION. By Henry Rose.* 
An emission of light has often been noticed during crystal- 
lization, but its appearance has always been a casual one, and 
never, as far as I am aware of, has it been produced at will. I 
have observed, during the crystallization of arsenious acid, a 
strong emission of light, which differs from that seen during 
the crystallization of other substances, inasmuch as it may be 
produced at pleasure. Take two or three drachms of the trans- 
parent or vitreous arsenious acid, put it in a mattress of white 
glass along with an ounce and a half of not fuming muriatic 
acid of the common strength, and half an ounce of water; allow 
the whole to boil for ten minutes or a quarter of an hour, and 
then let it cool as slowly as possible, which is best done by 
gradually decreasing the flame of the spirit lamp which had 
been used for the boiling. If the experiment is conducted in 
a dark room, the crystallization is accompanied by a strong 
emission of light, the formation of each little crystal being at- 
tended by a spark. If the vessel is then agitated, a great 
number of crystals suddenly shoot up, and an equal number of 
sparks occur at the same time. If a considerable quantity of 
arsenious acid, such as an ounce or an ounce and a half, or 
more, is treated with a corresponding quantity of diluted mu- 
riatic acid, then, on shaking the vessel, if the right moment be 
seized, the emission of light from the shooting of the crystals 
is so powerful that a dark room may be lighted up by it. 
Considerable time elapses before the acid solution of arseni- 
ous acid leaves off depositing crystals, consequently the cooled 
solution still continues to emit light on the second and even 
on the third evening, but only extremely feeble, and only 
when it is agitated. It is, however, impossible after this to 
produce any emission of light; a proof that it is occasioned by 
* Read to the Academy of Sciences at Berlin, July 30, 1835. 
