MOLLUSGCA. 39 
mantle, a thick vein of a yellowish white hue, filled 
with a substance resembling cream: this is the 
dye in question. It is thick and glutinous, so that 
you cannot well apply it with a pen; but with a 
camel’s-hair pencil you may paint, as it were, upon 
linen or cotton cloth any lines, the initials of your 
name, for example. When you have done this 
you will perhaps be disappointed, for the marks as 
they dry will be but just discernible, displaying 
only a pale yellow tint with not the slightest 
approach to purple, but exhaling an insufferable 
odour of garlic. 
Place your linen in the light of the sun, and look 
at it again in half-an-hour, or, if you please, watch 
its changes. ‘The marks have by this time passed 
from yellow into pea-green, and are now of a full 
grass-green; under the influence of the light the 
change proceeds rapidly, the yellow element gradu- 
ally disappearing, and the blue element becoming 
more and more prominent, until through the stages 
of deep-green, sea-green, and greenish-blue, the 
colour at length appears a full indigo. The red 
element now begins to be apparent, and rapidly 
increases in intensity until the hue is a dull, 
reddish purple. In my own experiments this was 
the ultimate tint obtained; a tint perfectly indelible 
as long as the texture of the material remained, 
neither light, nor time, nor washing, nor the appli- 
cation of chemical agents having now the least 
influence either in changing its hue or causing it 
to fade. I have seen it stated that if the cloth be 
washed in scalding water and soap, it comes out 
from the lather changed from the reddish purple 
hue to a fair bright crimson; with me, however, 
the soap and the hot water had no appreciable in- 
