urprising
miracle they praised God."

TIN.--We have no positive evidence as to whether the ancients used
oxide, or the salts of tin, in their dyeing operations. A modern dyer
could hardly produce permanent tints with some of the dye drugs named
without tin salts. We know that the ancients used the oxides of tin
for glazing pottery and painting; they may therefore have used salts
of tin in their dyeing operations. However, they had another
salt--sulphate of alumina--which produces similar results, although
the moderns in most cases prefer tin, as it makes a more brilliant and
permanent tint.

ALUM.--This is what is termed a double salt, and is composed of
sulphate of alumina and sulphate of potash. The process of
manufacturing it in this country is by subjecting clay slate
containing iron pyrites to a calcination, when the sulphur with the
iron is oxidized, becoming sulphuric acid, which, combining with the
alumina of the clay, and also with the iron, becomes sulphate of
alumina and iron; to this is added a salt of potash, which, combining
with the sulphate of alumina, forms the double salt alum. Soda or
ammonia may be substituted for potash with similar results; the alum
is crystallized from the solution. That the ancients were acquainted
with this double salt has been disputed, but we think there can be no
doubt of its existence and use at a very early period. A very pure
alum is produced in volcanic districts by the action of sulphurous
acid and oxygen on felspathic rocks, and used by the ancients for
different purposes. Pliny mentions _Alumine_, which he describes as
white, and used for whitening wool, also for dyeing wool of bright
colors. Occasionally he confounds this salt with a mixture of sulphate
of alumina and iron, which, in all probability, was alum containing
iron, the process of separation not being perfect; and he mentions
that this kind of alumen blackens on the application of nut-galls,
showing that iron was in it. Pliny says of alumen, that it is
"understood to be a sort of brine which exudes from the earth; of
this, too, there are several kinds. In Cyprus there is a white alumen,
and another kind of a darker color; the uses of these are very
dissimilar, the white liquid alumen being employed for dyeing a whole
bright color, and the darker, on the other hand, for giving wool a
tawny or sombre tint." This is very characteristic of a pure aluminous
mordant, and of one containing iron. He also ment