The e2ects of nitrifying bacteria can also be seen on stone.
The source of energy for these bacteria is not only reduced
nitrogen compounds deriving from soil, but also bird excrement
on elevated stone elements. Nitrifying bacteria cause
the formation of nitric acid, which dissolves limestone and
also sandstone with a calcareous binder. Calcium nitrate, unlike
calcium sulphate, is easily soluble in water, and that is
why the common nitri;ers leave traces on stone in the form
of lacunae and caverns. This kind of damage can be seen on
elevated parts of monuments and buildings.