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24 The Past and Present of Chemistry. [Jan., 
present state of chemistry that we should know what were the 
grounds of the belief that one metal could be transformed into 
another. 
The foundation of this belief was a theory of the cause of dif- 
ference in matter, which finds its best expression in the doctrine of 
Aristotle already alluded to, that matter itself is everywhere one 
and the same thing, and that its varieties are produced solely by a 
variation of its qualities. Changes in the properties of substances, 
and especially of metals, were recognized at an early period. Thus 
it was known that, by the action of certain substances, copper could 
be made as yellow as gold, and, by that of others, as white as silver, 
the transformation being effected throughout the entire mass. We 
now know that when red copper is turned into yellow copper (brass) 
or into white copper (German silver), a change takes place in the 
composition as well as in the colour; but at the period when 
alchemy flourished, such a change was not thought of any more 
than we now consider it as taking place when soft steel is trans- 
formed into hard steel—a transformation with which the ancients 
were also acquainted. The hardness, colour, ductility, fusibility, 
and some other properties of certain metals could be altered, and 
hence it was thought that it must be possible so to change all the 
properties of one metal into those of another, that the one metal 
would reaily be transformed into the other. Until the fifteenth 
century, and even somewhat later, the idea underlying the pursuits of 
alchemy, was the existence of an universal matter which, endowed with 
various properties, forms all known substances, and consequently 
all the metals; in short, that a change in appearance constitutes 
a veritable transformation of a metal. If a fragment of iron be 
dropped into a solution of blue vitriol, the iron gradually disappears 
and in its place we find copper. We now know that the iron is 
dissolved and the copper contained in the vitriol precipitated ; we 
do not regard the visibly iron-coloured metal, which is dropped into 
the solution, as including the same matter as the visibly copper- 
coloured metal which is afterwards found in its place, but in the 
alchemical stage of the science a totally different view prevailed, and 
the mythological nomenclature then used, such as Mars for iron, 
and Venus for copper, clearly expresses the then prevailing theory. 
The same material which in Mars’s coat of mail appeared as iron, 
reappeared in the garb of Venus (as copper) after beimg acted upon 
by the vitriol. 
In the sixteenth century chemistry emerged from its previous 
degraded condition, and passed into the hands of men who were 
not trammelled by the doctrines of Aristotle. The physicians who 
were the followers of Paracelsus paid but little respect to ancient 
authorities, and relied entirely upon their own observations and 
investigations. Three properties of matter especially excited their 
