285 
“ This mineralizing operation is performed by heat or fusion ; and 
there is no person skilled in chemistry, that will pretend to say this 
may be done by aqueous solution*.” 
Professor Playfair, who has given his powerful support to Dr. 
Hutton’s theory, speaking of these substances, metals in the form 
of an ore, mineralized by sulphur, says, “ Their union with this 
latter substance can be produced, as we know, by heat, but hardly 
by the way of solution, in a menstruum ; and certainly not at all, 
if that menstruum is nothing else than water. The metals, therefore, 
when mineralized by sulphur, give no countenance to the hypo- 
thesis of aqueous solution : and still less do they give any, when 
they are found native, as it is called, that is, malleable, pure, and 
uncombined with any other substance. The great masses of native 
iron found in Siberia, and South America, are well known ; and 
nothing certainly can less resemble the products of a chemical pre- 
cipitation. Gold, however, the most perfect of the metals, is found 
native most frequently : the others more rarely, in proportion nearly 
to the facility of their combination with sulphur. Of all such spe- 
cimens it may be safely affirmed, that if they have ever been fluid, 
or even soft, they must have been so by the action of heat ; for to 
suppose that a metal has been precipitated, pure and uncombined, 
from any menstruum, is to trespass against all analogy, and to main- 
tain a physical impossibilityf.” 
In a science like chemistry, in which, from the multiplicity of its 
subjects, and of their operations upon each other, important dis- 
coveries are daily being made, change of opinion must, necessarily, 
be frequently submitted to, by the most intelligent. Hence also it 
happens, that apparently established theories, of the most learned 
men, are sometimes subverted by those whose general knowledge 
* Theory of the Earth, vol. i. p. 63. 
f Illustrations of the Huttonian Theory, p. 58. 
