MURICIDJC. WHELK. 201 



green, which quickly deepens into an emerald green, 

 then changes to blue, and at last to a fine purplish-red. 

 If the cloth be now washed with scalding water and 

 soap, and laid again in the sun, the colour changes 

 to a beautiful crimson, which suffers no further altera- 

 tion from sun, or air, soap, alum, alkaline leys, or any 

 of the substances used for assaying the permanency of 

 colours. 



The juice of the purple-fish receives no colour itself, 

 and communicates none to silk or linen, without ex- 

 posure to the sun. It seems to be the light, and not 

 the heat, of the sun, that calls forth the tincture ; for 

 when the cloth is covered with thin opaque bodies, 

 which transmit heat without light, no colour is produced, 

 while transparent ones give no impediment to its pro- 

 duction. The juice, itself, in close glass vessels becomes 

 presently purple in the sun.* Lister, in 1686, mentions 

 the discovery of a shellfish, Purpura Anglicana, on the 

 shores of the Severn, in which there is a vein containing 

 a juice giving the delicate and durable tincture of the 

 rich Tyrian purple. A writer in the ' Annual Register ' 

 for 1 760, says that, being " at a gentleman's house in 

 the west of Ireland, he took particular notice of the 

 gown of the lady of the house. It was a muslin flowered 

 with the most beautiful violet colour .... She told me 

 it wa,s her own work, and took me to the seaside, where 

 she gathered some little shells ; . . . beating them open 

 and extracting the liquor with the point of a clean pen, 

 she marked some spots directly before me." He adds : 

 " I suppose a hundred fishes would not produce a drop 

 as large as a pea." Richard of Cirencester also mentions 



* ' ISeumaim's Chemistry/ p. 510 ; the Memoirs of the French 

 Academy for 1730. See ' Philosophical Transactions/ .No. 178. 



