PIGMENTS 163
lis, soap, and most acids, and is only destroyed by hot nitric acid or chlorine. It is
insoluble in most ordinary organic solvents, except hot aniline and nitrobenzene
(Friedlander, loc. «/., p. 768).
Pliny (see Bailey, I, 25-33) describes in some detail the source and method of
extraction, and says that the best quality was made at Tyre, probably the reason
why it is still called ' Tyrian purple ' (Laurie, The Pigments and Mediums of the
Old Masters^ pp. 47-62). This was the color in the togas of Roman emperors and
gave rise to the expression,' born to the purple.' It was used in the preparation of
a purple ink and in dyeing parchments upon which the codices of Byzantium were
written. Whelks that yield a purple dye are also found in waters of the British
Isles, and they furnished the purple color for some of the early English, Irish, and
French manuscripts (see Thompson, The Materials of Medieval Painting^ p. 156).
The color went out of general use about the VIII century, though it may have been
used occasionally up into the XII century (Thompson, loc. a/., p. 157).
Ultramarine Blue, artificial (French ultramarine, permanent blue). All the
ultramarine used in commerce is made artificially by a furnace process. In chemical
composition and structure it is identical with the natural ultramarine which is
made from the rare mineral, lapis lazuli (see Ultramarine Blue, natural). The
chemical composition of the mineral was first established by Desormes and
Clement in 1806 (see * Memoir sur POutremer,' Annales de Chimie [first series],
LVII [1806], pp. 317-326). They showed that it was essentially a compound of
soda, silica, alumina, and sulphur, and they predicted, on the basis of the analysis,
that artificial production should follow. Already blue masses had been observed
in ovens where the Leblanc soda process was being carried out (see Rose, p, 175)
and, in 1814, L. N. Vauquelin (' Note sur une couleur bleue artificielle analogue
a Toutremer,' Annales de Chimie [first series], LXXXIX [1814], pp. 88-91) de-
scribed a blue substance taken from the hearth of a demolished soda furnace by
M. Tessaert at the glass works of St Gobain, and showed that it was quite similar
in composition and properties to ultramarine from lapis lazuli. In November, 1824,
the Societe d^ Encouragement pour TIndustrie National offered a prize of 6000 francs
for a method for making artificial ultramarine at a cost not to exceed 300 francs
per kilogram. The prize was awarded four years later to J. B. Guimet in Toulouse
for his method of preparing artificial ultramarine which he asserted he had
developed in 1826 and had not published, but had kept a secret. Almost simul-
taneously and quite independently, Christian Gmelin of Tubingen, and F. A.
Kottig of Meissen, perfected processes for the same purpose, Very soon after 1830,
factories were established in France and Germany where it came principally to be
made, although later it was also manufactured in England, Belgium, and the
United States.
Two distinct kinds of ultramarine are made. ' Soda ultramarine * is made by
heating in closed fire clay crucibles in a muffle furnace, a finely ground mixture of
China clay, soda ash, coal or wood charcoal, silica, and sulphur. After maintaining