106 
THE PRINCIPAL FLOOR. 
origin of amber is inferred from its resemblance to certain recent 
resins, from its association with lignite, and from the occurrence 
of insects and other organic enclosures. Goppert named the 
tree supposed to have yielded most of the amber Pinites succinifer 
and Dana called the pure part of amber Succinite. The prin- 
cipal supply cf amber is obtained from the Prussian coast of 
the Baltic ; but specimens are occasionally found on the coasts of 
Norfolk and Suffolk. Some examples of amber from Cromer 
are here shown. A fluorescent variety found in Sicily, is known 
as Simetite . 
Case D. — Sulphur. 
Sulphur occurs chiefly in volcanic districts, such as Sicily 
and the Lipari Islands, and the Solfatara, near Naples. There 
are also important deposits in the Romagna and in Spain; 
whilst the sulphur of Iceland has also attracted attention, 
commercially. Most of the sulphur-yielding localities are well 
represented in the. Case before us, and several of them have 
contributed finely-crystallised specimens. 
The extraction of sulphur from the impure native materials, 
and the properties of the prepared sulphur, are also here 
illustrated. As native sulphur is usually contaminated with 
earthy matters, it is purified by a simple process of distillation. 
Sulphur is also largely extracted from iron pyrites (p. 75), a 
bisulphide of iron, which yields a considerable proportion of 
free sulphur on simple distillation. 
At 226° Fah, sulphur melts to an amber-coloured liquid ; if 
the temperature be then raised to about 400° Fah. it becomes 
dark brown, opaque, and thick ; but heated yet higher it again 
becomes thin and limpid. If the thick tenacious sulphur at 400° 
be suddenly cooled by immersion in water, it forms a soft and 
transparent mass of considerable elasticity, and in this state may 
be used, as shown here, for receiving impressions of seals, &c. 
The crystals of native sulphur, and those prepared by 
evaporation from solution at ordinary temperatures, are entirely 
distinct in form from the crystals which may be obtained by 
solidification from a state of fusion ; and this difference in 
crystalline character is accompanied by a corresponding variation 
in density and other physical properties. The sulphur is, in 
fact, dimorphous. 
With the sulphur-group will be found a fine specimen of the 
closely-allied but much less widely- diffused element, selenium , as 
prepared from the deposits of the copper-smelting furnaces of 
Mansfeld (p. 93). 
Case E. — Rock Salt and other Salts of Sodium. 
A specimen of crystallised sodium is placed here as representing 
the metallic base of the group of minerals which occupy this 
Case. Of these salts of sodium, the most important is the 
chloride or common salt. The greater part of our culinary salt 
