102 Sir Humphry Davy’s experiments and observations 
those in the vase and much brighter, and which had been 
employed in various apartments, and formed the basis of the 
colouring of the niche and other parts of the chamber in which 
the Laocoon is said to have been found. On scraping a little 
of this colour from the wall, and submitting it to chemical 
tests, it proved to be vermilion or cinnabar, and on heating 
it with iron filings, running quicksilver was procured from it. 
I found the same colour on some fragments of ancient stucco 
in a vineyard near the pyramidal monument of Caius Cestius. 
In the Nozze Aldobrandine, the reds are all ochres. I tried 
on these reds the action of acids, of alkalies, and of chlorine, 
but could discover no traces either of minium or vermilion in 
this picture. 
Minium was known to the Greeks under the name of 
crcivtyuxv},* and to the Romans under that of cerussa usta. 
It is said, by Pliny, - f* to have been discovered accidentally by 
means of a fire that took place at the Pirseeus at Athens. 
Some ceruse which had been exposed to this fire was found con- 
verted into minium, and the process was artificially imitated: 
and he states that it was first used as a pigment by Nicias. J 
Several red earths used in painting are described by Theo- 
phrastus, Vitruvius, § and Pliny. The Sinopian earth, the 
Armenian earth, and the African ochre, which had its red 
colour produced by calcination. 
Cinnabar or vermilion was called by the Greeks jc<wa£a^,|| 
and by the Romans minium. It is said by Theophrastus^ to 
have been discovered by Callias, an Athenian, ninety years 
before Praxibulus, and in the 349th year of Rome, and was 
* Dioscorides, Lib. v. 122. f Lib. xxxv. Cap. 20. 
I Pliny, Lib. xxxv. Cap. 20. § De Architectura, Lib. vii. Cap. 7. 
Dioscorides, Lib. v. Cap, 109. De Lapid. Cap. 104. 
