216 Rev. J. Barlow, [March 14, 



ther by their mutual cohesion, can be detached by mechanical means. 

 A comparison was made between this ore of gold and pure clay, the 

 ore of aluminium. Clay consists of silica and alumina (the oxide of 

 aluminium). In this substance, however, the silica combines as an 

 acid, so as to form a natural salt, from which the alumina, and then 

 the aluminium from the alumina, have to be successively separated, 

 not by mechanical force but by powerful chemical reagents. The 

 ore of gold occurs rarely, but is recognized at once by any experi- 

 enced eye ; the ore of aluminium is one of the most abundant 

 substances in nature, but its recognition as a metallic ore has 

 tasked the extreme attainments of modern science. 



{b) Iron, tin, antimony, and lead were next referred to as types 

 of the metals of the middle age. Their ores were exhibited. The 

 sapphire,* the purest form of corundum, which is native oxide of 

 aluminium, was contrasted with haematite, the native sesquioxide of 

 iron. The metallic aspect, characterizing the ores of this class of 

 metals, was noticed. This appearance must naturally have led to 

 these substances being subjected to the action of fire. The separa- 

 tion of a metal by the reducing action of the fuel of the furnace on 

 its ore, was illustrated by metallic lead, one of the ingredients of 

 flint glass, being made visible by the action of the flame of a spirit 

 lamp on a piece of that substance. Glass is a combination of silica 

 with oxide of lead and other metals; it therefore carries on the 

 analogy with pipe-clay, the silicate of alumina : but aluminium 

 cannot be reduced from the silicate of alumina by any known fuel, 

 at any known temperature. Were this not the case, crucibles, 

 furnaces, even houses which are made of clay, would be decom- 

 posed, and the aluminium they contain extracted, whenever they 

 were exposed to the force of a sufficiently intense combustion. 



(c) The metals of the scientific age. — These metals were 

 brought into visible existence by the pile of Volta. The searching 

 and separating properties of this wonderful invention were made 

 known at the commencement of the present century. Simulta- 

 neously with this discovery there commenced an age of research, 

 which began and is continued to this time in the Royal Institution. 

 It is characterized by the historian of the " Inductive Sciences,'* 

 as the epoch of Davy and of Faraday.f The knowledge and 

 sagacity of Davy induced that distinguished man to seek for an 

 alkaligen (or generator of alkali) at that (so called) pole of the 

 voltaic battery, where Nicholson and Carlisle had recently found 

 hydrogen (generator of water). This alkaligen was the metal of the 

 alkali — the metal of the scientific age. 



* Miss Coutts, M.R.I., kindly lent three sapphires of great size and beauty 

 to illustrate this discourse. It has been suggested that the characteristic 

 colour of these jewels may be due to the presence of a protoxide of alumi- 

 pium (Al O). 



t Whewell's Hist, of Induct, Sciences, Vol. iii. p. 178. 



