IIYDROPHANE. 
SPECIFIC CHARACTER. 
Opalus HYDROphanus. O. subopacus in liquidis pellucidus co- 
loremque mutans., linguae adherens. 
Linn. Syst. Nat. Gmel. 3. p. 1 5Q. 
Subopaque; but becomes transparent 
when immersed in liquids : adheres 
to the tongue. 
Achates unguium colore in aere opaca, 
aqua pellucens. Waller. Miner. 83. 
Syst. Miner. 1 . p. 283. no. 21. 
Lapide mutaeili. Bruckman. 
Hydrophane. . . . Cronst. Miner. 1 . p. 1/8. Kinvan, 
Miner. 1 . p. 295 . Patrin, Hist, des 
Miner. 2. p. 224. Brogn. Miner. 1 . 
P* 299 * 
This very singular stone has attracted the attention 
of naturalists, for the property which it exhibits of 
passing from an opaque to a transparent state after 
being laid in water for a few hours. We owe the 
discovery of this phenomenon to a German na- 
turalist, who, having several opals of a milky ap- 
pearance and without colour, thought to improve 
them by the assistance of acids: the event surprised 
him ; for he perceived that some of these stones, 
which were perfectly opaque before, became com- 
