Page:Natural History, Mollusca.djvu/58

46 same property.



This liquor must not be confounded with that which constitutes the purple dye of Murex, Purpura, &c. already mentioned, for it is so volatile as to be unsuitable for the purposes of dyeing. According to Cuvier, the secretion in drying assumes the beautiful deep hue of the sweet Scabious, and remains unaltered by long exposure to the air. Nitric acid, in small quantity, heightened the tint, but a larger dose changed it to a dirty orange colour, while potash turned it to a dingy vinous grey. Both the acid and the alkali precipitated many white flakes from the fluid. The purple tint is readily transferred to spirit when the animal is immersed in it; the tincture retains this colour for awhile, but at length becomes of a deep clear red, like that of port wine.

A very common shell in ponds and ditches, (Planorbis corneus,) coiled up like a ram's horn, is