366 SUPPLEMENT 
perfectly saturated, and all its parts completely exposed to 
the solar action, that the strongest lixivia, and most active 
_ tests, have no influence on the colour, except that when 
there remain many layers at the surface, the last having im- 
peded the solar action upon the others, and its combination 
with the tissue not having taken place, the colour then grows 
very clear, so that Duhamel concludes, from his experiments 
on the subject, that the ancients must have had a peculiar 
process for extending the colouring matter, which is always 
pretty thick and viscous in the animals, and thus making it 
penetrate into all parts of the tissue. Perhaps it was for this 
purpose that water, urine, and salt, were employed by the 
ancient dyers. ‘Templeman tells us, however, from his own 
experience, that the addition of salt has no effect. This is a 
subject for the analysis of chemists, who, nevertheless, appear 
to have bestowed but little attention upon it. It deserves 
investigation, not as regards the art of dyeing, for the purple 
of the moderns is as beautiful and as fixed as that of the 
ancients, more easy to be obtained, and consequently less ex- 
pensive—but it is important to the science of animal chemistry. 
Duhamel thinks that the action of the sun in purpurification 
is somewhat analogous to what passes in the coloration of 
fruits which remain whitish, yellow, or green, in shady places, 
and are coloured only where the action of the sun is received. 
Here, however, the change is slow and gradual, but in the 
purple it takes place instantaneously. 
From all that has been investigated respecting this subject, 
M. de Blainville draws the following conclusions. 
1. That it is probable, that the molluscum from which the 
ancients principally derived their purple, is an animal toler- 
ably large, known in the Mediterranean, perfectly described 
by Columna, and of which Linneus, and the modern concho- 
logists make their murex trunculus, or perhaps the murex 
brandaris. 
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