SULPHATES AND PHOSPHATES. 93 



lazuli furnished the once costly pigment ultramarine ; but 

 by the discovery of a method of producing an artificial and 

 cheap form of the latter, the use of the mineral as a pigment 

 has almost ceased. 



The sulphates of strontium, Celestite (35c), of barium, Barytes Sulphates, 

 or Heavy Spar (36a), and of lead, Anglesite (36e), are all repre- gjg"^^ * *^' 

 sented by series of specimens. 



Gypsum, or Selenite (36f), is a sulphate of the metal calcium: 

 when heated, it gives up its water of crystallisation and falls to 

 a white powder, known as "Plaster of Paris," which, when 

 moistened, again combines with water and yields a coherent 

 solid. Gypseous alabaster, a massive variety of gypsum (36h), 

 owing to its whiteness, iine texture, and softness is used as a 

 material for statuettes and other indoor ornaments. Oriental, 

 alabaster is a harder substance, stalagmitic calcite, the carbonate 

 of calcium. 



Borax (37c), a borate of sodium, is much used as a flux, also 

 in soldering, and in the preparation of easily fusible enamels. 

 It was formerly carried over the Himalaya on sheep and 

 goats from a lake in Tibet, but is now obtained largely from 

 the borax-lakes of the United States, and is also extensively 

 prepared from the boracic acid lagoons in Tuscany. 



Nitratine or Soda-nitre (37d), found in Chili in beds of large 

 extent, is largely used for the preparation of nitric acid and of 

 saltpetre, and also as a fertiliser. 



Calaite or Turquoise (38g), a phosphate of the metals alu- 

 minium and copper, does not occur in the crystalline state. 

 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 being chiefly 

 brought from the turquoise-mines not far from Nishapur, 

 in Persia. 



As a supplement to the collection of simple minerals, is 

 arranged, in case 41, a group of natural substances which 

 either belong or are closely related to the Mineral Kingdom, 

 although, in the formation of most, organised matter has played 

 a very important part. The most important members are Coal 

 and Amber. Coal (41a), in most of its varieties, gives structural 

 evidence of its vegetable origin; its chemioal composition 



