372 
POPULAR SCIENCE REVIEW. 
action of the sea — for the treasure which Anson failed to capture, sunk by 
the Spaniards from their argosies, was found, after some time, to be coated 
with the chloride. While gold for ever would withstand the action of wind 
and wave, and only passes through the furnace to be purified and exalted 
from its fires. Undimmed by the breath of Time, unharmed by the wear of 
centuries, unaffected by the all-conquering oxygen, the metal first dug from 
the bed of the Euphrates, or quarried from the caverns of Ophir, is still 
fresh and brilliant as the glittering coinage of to-day ! 
The advancement of chemical science has, while leading us into a clearer 
knowledge of the properties of the metals, naturally taught us to investigate 
the various phenomena which accompany their extraction from the elements 
with which they were in intimate association, and the subject has proved so 
inviting that many philosophers have devoted yearn of laborious life to this 
special branch of technology. The work now before us offers a fair example 
of what long continued and patient experiment can effect ; and the subject 
has evidently so grown under the author’s hands, that, although we believe it 
was his original intention to comprise the whole matter in one volume, that 
which is already published only treats of two metals and their compounds, 
together with an elaborate treatise on Fireclays and Fuel. Another volume 
is promised shortly, which, it is stated, will conclude the work ; but if we are 
not much mistaken, two or more will not contain all the important particu- 
lars the author has at his command, as we have yet to become acquainted 
with iron, lead, silver, gold, platinum, nickel, cobalt, arsenic, bismuth, anti- 
mony, tin, and mercury, all of which possess a very high, although not perhaps 
an equal interest. 
Dr. Percy commences his introductory chapter by showing that a sound 
knowledge of chemical and physical laws is essential to the full understanding 
of any metallurgic process, and as an illustration, the ordinary system of 
copper smelting is adduced : “ When an ore of copper, consisting essentially 
of copper, iron, sulphur, and silica, is subjected to a series of processes, such 
as heating with access of air under special conditions, melting, &c., copper is 
separated in the metallic state. The sum of these processes is termed the 
smelting of copper. In this operation of smelting, certain chemical changes 
take place. The sulphur combines with the oxygen of the air, and is evolved 
chiefly as sulphurous acid ; the iron is similarly converted into oxide, which 
combines with the silica present, to form a fusible compound or slag. There 
are thus several facts which are proved on chemical evidence. These facts, 
when systematically arranged, may be said to constitute the scientific know- 
ledge of copper smelting ; and that knowledge necessarily implies a know- 
ledge of the chemical relations of copper, iron, sulphur, oxygen, and silica to 
each other. There are many other facts coimected with copper smelting, but 
those mentioned suffice for the present purpose of illustration. The man 
who conducts the process of copper smelting in ignorance of these facts, has 
simply an empirical, in contradistinction to a scientific, knowledge of the 
art.” 
We are then led on to the physical properties of the metals, the action of 
heat, the fixed and the volatile metals, specific gravity, crystallisation, varieties 
of fracture, malleability, ductility, tenacity, toughness, softness, the rela- 
tive power of conducting heat and electricity, &c. ; and under this last head 
