612.
The specific and proper terms in use might, however, still be conveniently employed, and we have thus made use of the words orange and violet. We have in like manner employed the word "purpur" to designate a pure central red, because the secretion of the murex or "purpura" is to be carried to the highest point of culmination by the action of the sun-light on fine linen saturated with the juice.
L.
MINERALS.
613.
The colours of minerals are all of a chemical nature, and thus the modes in which they are produced may be explained in a general way by what has been said on the subject of chemical colours.
614.
Among the external characteristics of minerals, the description of their colours occupies the first place; and great pains have been taken,