304 NATURAL HISTORY OF PRECIOUS STONES, &c
ing curious passage (Ep. 90, 33) :—" The same Democritus discovered the method of softening ivory; and how a pebble by means of boiling can be transformed into an Emerald, by
which same process (coctura) artificial gems continue to be stained at
present." This looks like an allusion to the staining of crystal, "
calculus " being usually applied to a white quartz pebble, such as
Pliny notices as ingredients in glass-making.
De
Boot (II. 53) runs up a long list of the virtues of the Emerald, as
then firmly believed in by everybody, himself included—Worn in a ring
it was a sure preservative against epilepsy (as Marbodus also teaches
upon the authority of Aristotle), cured dysentery, and preserved the
chastity of the wearer, or else betrayed and punished its violation by
immediately flying into pieces.* The imperial physician gives a recipe
for preparing the " Tinctura Smaragdi " —a most efficacious medicine in
dysentery, epilepsy, and malignant fevers : " Pound the Emerald in an
iron mortar, sift the powder through muslin, then cover it with spiritus urinae (sal
volatile) : the spirit must be distilled off, leaving the powder of a
grey colour, but which will communicate that of the emerald to spirits
of wine."
The
value of this stone in the middle ages was enormous. Fran. Maria,
prince of Urbino, paid 113 gold pieces for an Oriental Emerald weighing
no more than two carats. Cellini puts it at 400 gold scudi the carat,
or at four times
