PROCEEDINGS OF GEOLOGICAL SOCIETIES. 
147 
be volatilized, especialh' by the agency of steam. Every chemist knows 
that boracic acid, which is a fixed body, may, by the agency of steam, be 
vaporized to a considerable extent. A case of the volatilization of flint 
was recorded some years ago by iMr. Julius Jeffreys. It occurred in a 
potter's kiln in India. His statements have been repeated by many jour- 
nalists, both British and foreign. It is important that we should examine 
the ground upon which he arrived at his conclusion. He allowed a large 
quantity of steam to pass through a potter's kiln, of which the tempera- 
ture more than sufficed to melt pig-iron, and he afterwards observed round 
the opening of the kiln from which the steam escaped, several pounds of 
silica deposited in the form of snow. In commenting upon this statement, 
Berzelius, who accepted it, adduces as a parallel case the well-known vola- 
tility of boracic acid under the same conditions, and the fact observed by 
Gaudin concerning the volatilization of silica when melted before the 
oxy-hydrogen blowpipe. Now, the lecturer had examined all the original 
statements concerning this allegation, and he must say that the conclusion 
to which he had arrived is, that it is altogether unsatisfactory. There is 
no proof whatever, or, at all events, there is none advanced, that the de- 
posit was silica at all. No analysis was made, and no man is justified, 
w ithout the evidence furnished b}' analysis, in pronouncing definitely upon 
a point of this kind. Secondly, admitting that the substance called silica 
w as really silica, there is no evidence to show that it was volatilized in the 
way described. We perfectly well know that in metallurgical operations 
a very large amount of finely-divided matter may be carried to a very 
long distance mechanically by gases or vapours floating over it. Volatili- 
zation is something different from the mechanical removal of the particles 
of a substance. 
The subject next taken up was one of great interest —aluminium. This 
aluminium plays a most important part in this world, so far as the forma- 
tion of the crust of the earth is concerned. It is one of the chief consti- 
tuents of, and forms an essential part of, all clay. It exists almost every- 
where in a greater or Jess proportion. It is undoubtedly one of the most 
beautiful elements of which this world is formed, or the external part of 
it rather. 
Aluminium has of late excited a great deal of attention. Formerly it 
was known only very imperfectly, a few grains only having been obtained, 
now it is produced by the hundredweight. The metal has a bluish-grey 
colour, — intermediate between tin and zinc in point of colour, being not 
so white as tin, and less blue than zinc. It is by far the lightest of all 
metals now used in the arts, its specific gravity being in round numbers 
2-5 ; that is to say, whatever measure of water weighs 1, the same measure 
of aluminium will weigh 2 o. 
Aluminium has a most powerful affinity for oxygen. When combmed 
with that element, it constitutes the well-known base alumina. Like sili- 
con, although it lias this strong allinity for oxygen, yet when we succeed 
in detaching it from oxygen, and obtaining it in a compact, solid form, it 
is remarkably stable, and mit^ht be exposed indefinitely to the air without 
undergoing oxidation to any extent. When melted, it oxidizes on the 
surface and forma alumina. This acts as a coating, and protects the sub- 
jacent molten metal from further oxidation. . . 
Aluminium is obtained from a salt termed chloride of aluminium, it 
we take alumina, which is aluminium and oxygen, and heat it with charcoal 
even to a high temperature, we cannot, sa far as we know, succeed in 
eliminating the oxygen and detaching the aluminium; but if we make the 
