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this is precisely the moment they believe they have arrived
at the goal they aspire to, when in truth they find themselves
at the greatest distance from it ; because these different ox-
ides, instead of giving such and such a colour, give quite the
contrary ; above all it is the yellow colour which it is diffi-
cult to obtain, because it is that which is most wanted to col-
our incorruptible teeth.
They have not only consulted the treatises on chemistry,
of existing authors, who have equally indicated the means to
be employed, but, it must be confessed they have not been
specially occupied in this particular ; they consequently have
given incorrect information.
I have in my hands the note of a celebrated chemist, which
proves he was solicitous for the interest of the public, but did
not think proper to occupy himself with this branch of chem-
istry, which furnishes dentists with the means of perfecting
a very important part of their art.
From what we have just said, it follows that the study of
chemical works has not furnished, and cannot furnish, in ef-
fect, to the dentist but general ideas on the combination and
manipulation of the earths and oxides ; to succeed they must
make numberless attempts, and must have sufficient know-
ledge of chemistry to make them profitable ; without that, he
ought not to expect to make incorruptible teeth of the proper
kind.
How much trouble have I not had to arrive at one hope-
ful point ! how many fruitless trials have I not made ! but
the more obstacles I had to surmount, the more the reader
may have confidence in the formulas I present him. In ef-
fect, there is not one which does not give, in its result, the
colour which I speak of; if it is not so, the fault will be in
the bad quality of the substances employed. The kaolin and
petunze sometimes contain foreign substances, which change