PROCEEDINGS OE GEOLOGICAL SOCIETIES. 



147 



be volatilized, especially 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 Mr. 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, 

 without the evidence furnished by analysis, in pronouncing definitely upon 

 a point of this kind. Secondly, admitting that the substance called silica 

 was 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 pla}^s 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 less 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 

 25 ; that is to say, whatever measure of water weighs 1, the same measure 

 of aluminium will weigh 2*5. 



Aluminium has a most powerful affinity for oxygen. When combined 

 with that element, it constitutes the well-known base alumina. Like sili- 

 con, although it has this strong affinity for oxygen, yet when we succeed 

 in detaching it from oxygen, and obtaining it in a compact, solid form, it 

 is remarkably stable, and might be exposed indefinitely to the air without 

 undergoing oxidation to any extent. When melted, it oxidizes on the 

 surface and forms 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. If 

 we take alumina, which is aluminium and oxygen, aud heat it with charcoal 

 even to a high temperature, we cannot, so far as we know, succeed in 

 eliminating the oxygen and detaching the aluminium; but if we make the 



