54 
EAST WING. 
costly pigment ultramarine ; through the discovery of a method 
of producing an artificial and cheap form of the same material, 
the use of the mineral as a pigment has been quite superseded. 
The sulphates of strontium, Celestine (35c), of barium, Barytes 
or Heavy Spar (3()a), and of lead, Anglesite (36e), are all repre- 
sented by long series of specimens. 
Gypsum or Selenite (36f) is the hydrated sulphate of lime : 
when heated it gives up its water of crystallisation and falls to a 
white powder, known as Plaster of Paris " ; when moistened 
the powder again combines with water and forms a coherent 
solid. A magnificent crystallised specimen, a gift from the late 
Prince Consort, will be found in the Pavilion. Gypseous ala- 
baster is a massive variety of gypsum (36h); owing to its wliite- 
ness, fine texture, and softness, it is largely used as a material 
for statuettes and other in-door ornaments; the Oriental ala- 
baster is a harder substance, stalagmitic calcite, the carbonate 
of lime. 
Borax (37c) is a hydrated borate of sodium. It is much used 
as a flux, also in the process of soldering, and in the preparation 
of easily fusible enamels. It was formerly carried over the 
Himalayas from a lake in Thibet, but is now obtained largely 
from borax lakes of the United States, and is extensively pre- 
pared from the boracic acid of the lagoons in Tuscany. 
Mtratine or Soda nitre (37d) is found in beds extending for 
many miles ; it is used for the preparation of nitric acid and of 
saltpetre. 
Calaite or Turquoise (38g) is a hydrated phosphate of alumi- 
nium ; it owes its blue or green colour to the presence of small 
quantities of salts of copper and iron. Being as hard as felspar 
and taking a good polish, it has been much, prized in jewellery 
under the name of Oriental Turquoise ; that which comes into 
the market is chiefly brought from the turquoise mines, not far 
from Nishapur, in Persia. 
As a supplement to the collection of simple minerals, there is 
arranged, in cases 41 and 42, a group of natural substances 
which either belong or are closely related to the Mineral King- 
dom, although in their formation organised matter has played a 
very important part. The most important members are Coal 
and Amber. 
