e away the purity and
plainness of the water. Therefore pure and plain water is not
necessary for Baptism.

Obj. 3: Further, the water that flowed from the side of Christ
hanging on the cross was a figure of Baptism, as stated above (A. 3,
ad 3). But that water, seemingly, was not pure, because the elements
do not exist actually in a mixed body, such as Christ's. Therefore it
seems that pure or plain water is not necessary for Baptism.

Obj. 4: Further, lye does not seem to be pure water, for it has the
properties of heating and drying, which are contrary to those of
water. Nevertheless it seems that lye can be used for Baptism; for
the water of the Baths can be so used, which has filtered through a
sulphurous vein, just as lye percolates through ashes. Therefore it
seems that plain water is not necessary for Baptism.

Obj. 5: Further, rose-water is distilled from roses, just as chemical
waters are distilled from certain bodies. But seemingly, such like
waters may be used in Baptism; just as rain-water, which is distilled
from vapors. Since, therefore, such waters are not pure and plain
water, it seems that pure and plain water is not necessary for
Baptism.

_On the contrary,_ The proper matter of Baptism is water, as stated
above (A. 3). But plain water alone has the nature of water.
Therefore pure plain water is necessary for Baptism.

_I answer that,_ Water may cease to be pure or plain water in two
ways: first, by being mixed with another body; secondly, by
alteration. And each of these may happen in a twofold manner;
artificially and naturally. Now art fails in the operation of nature:
because nature gives the substantial form, which art cannot give; for
whatever form is given by art is accidental; except perchance when
art applies a proper agent to its proper matter, as fire to a
combustible; in which manner animals are produced from certain things
by way of putrefaction.

Whatever artificial change, then, takes place in the water, whether
by mixture or by alteration, the water's nature is not changed.
Consequently such water can be used for Baptism: unless perhaps such
a small quantity of water be mixed artificially with a body that the
compound is something other than water; thus mud is earth rather than
water, and diluted wine is wine rather than water.

But if the change be natural, sometimes it destroys the nature of the
water; and this is when by a natural process water enters into the
substance of