REVIEWS. 
371 
In short, that the whole world itself, from the summit of its loftiest cordillera 
to the seething mass within its centre, was one vast sphere of metal, tarnished 
and dimmed by contact with surrounding elements. 
And our forefathers, probably, distinguished the few metals with which 
they were acquainted more by their physical than their chemical charac- 
teristics. They knew that lead had not the lustre of silver, nor the latter 
the yellow gleam of gold, nor gold the reddish hue of copper ; that tin was 
too soft a material from which to form the offensive spear or the peaceful 
praning-hook, the weapon of the warrior or the implement of the husband- 
man ; and that hard, enduring iron must serve the soldier in the conflict and 
the farmer at the plough ; but they knew not the salts or the chemical com- 
pounds of the metals. Were those metals disguised, as they are in solution, 
they could not distinguish them from one another. 
Modern chemistry teaches us to investigate these matters more closely, not 
to be content with the condition of a metal in its elementary form, but to 
understand the reaction it imparts when in combination with other bodies, 
and hence by certain and unerring tests to be able to affirm its presence, 
even when its metallic form is hidden from our eyes. Knowing the charac- 
teristic colours which the metal chromium can yield to certain transparent 
minerals, we can recognize its acid blazing in the ruby, or its oxide gleaming 
in the emerald’s milder light ; or cobalt, in the sapphire glass of some old 
cathedral ; or manganese, in the amythestine spars of Derbyshire. Every 
metal can be known by certain phenomena which always accompany its 
combination, by the colour it gives to fluxes, or by the tints it imparts to 
flame. 
During the last century, what numerous metals have been brought to 
light ! The ancients recognized seven only — we are acquainted with about 
fifty ; and the increased range of our experience has led us to alter, in 
certain respects, our preconceived notions of their characteristics. Metals 
were always described in earlier treatises as essentially heavy bodies, having a 
far higher specific gravity than water, but science has given us several which 
are much lighter than that liquid (such as potassium, sodium, and lithium) ; 
in many points, however, such as being good conductors of heat and 
electricity, they possess properties in common. Their chemical, as well as 
their physical characters are exceedingly diverse, some combining with 
oxygen with such avidity, even at ordinary temperatures, as to lose their 
metallic appearance after a few moments’ exposure to the atmosphere, whilst 
others can be submitted to the strongest heat for many hours without 
suffering any change. It is interesting to trace these phenomena, as exem- 
plified in the various metals, beginning with potassium and terminating, 
perhaps, with platinum or gold. Potassium, even in dry air, is soon con- 
verted into potash, and, as far as its metallic nature is concerned, would 
instantaneously perish in the dewdrop. Magnesium, although not so strongly 
affected, burns in the flame of an ordinary candle, emitting, during its com- 
bustion, the most vivid and beautiful light. Iron, the vety symbol of 
enduring strength, speedily becomes oxidized, and, unless carefully shielded 
from external influences, rusts into the earth from whence it came. Copper, 
although in a less degree, soon becomes tarnished and grows dim. Even 
silver loses its lustre after the lapse of years, and cannot withstand the 
no. in. 2 c 
