While the product of water steeped in clean tan bark may be favorable
in its action upon boiler incrustation, _it has been found to be very
unsafe, in practice, to use the “tan liquor” taken from the vats_.
The danger arises from the fact that sometimes during the process of
tanning leather, the required acidity cannot be produced by natural
fermentation when sulphuric acid is added, in order to bring the liquor
to its required strength—in due course, this corrosive substance acts
injuriously on the boiler.