43 
combined with hydrogen by applying heat to a 
mixture of fluor or Derbyshire spar and sulphuric 
acid ; and in this state it is an intensely acid com- 
pound, a little heavier than water, and which be- 
comes still denser by combining with water. The 
existence of fluorine as an element is proved by 
its expulsion from certain compounds by chlorine, 
and by its transference from place to place. In 
attempts made to confine it, so as to examine its 
properties, it always combines with, or decom- 
poses the vessels employed, so that, as yet, its 
physical qualities are unknown : 1 6 is an ap- 
proximation to the number representing it. 
4. Iodine . This substance is procured from the 
ashes of marine plants, after the extraction of the 
carbonate of soda, by acting upon them by sul- 
phuric acid. It appears as a dark-coloured solid, 
having the colour and lustre of plumbago : its 
specific gravity is about 4, that of water being 1. 
It fuses at a low temperature, and at a heat about 
that of boiling water, becomes a violet-coloured 
gas. It forms an active acid by uniting to 
hydrogene. The alkaline metals burn, when 
heated in it. It unites to all the metals upon 
which its action has been examined, 
5. Brome. This body has been very recently 
discovered in sea water. It is in its nature analogous 
to iodine, and resembles a compound of these two 
bodies. It is a dense liquid, and forms an orange- 
coloured gas by a gentle heat. 
6. Hydrogene , or inflammable air, is the lightest 
known substance ; its specific gravity is to that of 
air as 732 to 10000. It burns by the action of an 
