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ARTIFICIAL ULTRAMARINE. 
proportions. Native ultramarine is procured from the lapis 
lazuli, — the artificial kind, according to Rohiquet's process, 
is made by heating to low redness a mixture of one part 
of porcelain clay, one and a half of sulphur, and one and a 
half parts of anhydrous carbonate of soda, in a covered cru- 
cible so long as vapours are given off. When opened, the 
crucible is usually filled with a spongy mass of a deep blue 
colour, containing more or less ultramarine, mixed with the 
excess of sulphur employed, and some unaltered clay and 
soda. The results are, however, by no means uniform. 
The price of the native ultramarine was formerly five 
guineas an ounce, the artificial is sold at a few shillings an 
ounce, and is equally durable. 
The colour of both is destroyed by nitric acid, or by a 
long-continued full red heat. Hence the difficulty in pre- 
paring the artificial variety. The destruction of the colour 
by nitric acid renders it easy to detect the admixture of 
cobalt, or Prussian blue, with ultramarine. The presence 
of indigo would be found by the use of sulphuric acid, 
which destroys the ultramarine and dissolves the indigo 
unchanged in colour. Strange as it may appear, even the 
artificial ultramarine is now largely adulterated. A speci- 
men, lately examined by M. Chevalier, was found to con- 
tain forty per cent, of blue carbonate of copper. This is 
decidedly injurious, because the blue colour of copper, under 
exposure to air and light, slowly becomes green. 
The discovery of artificial ultramarine was accidentally 
made by Vauquelin, in 1S14. It was found on pulling 
down a soda factory, where sulphate of soda had been fused 
with charcoal, that some parts of the walls had a rich blue 
colour. This intelligent chemist examined the substance, 
and ascertained that it was identical in composition with 
ultramarine. Prizes were offered in France for a chemical 
process for its preparation ; and the result was that methods 
were discovered about the same time by M. Guimet, Paris, 
andM. Gmelin, of Tubingen. The process of Robiquet above 
