as a contamination of the tar-oils.

_Applications of Coal-Tar in the Crude State._--Large quantities of
coal-tar are employed for various purposes without submitting it to the
process of distillation. It is mostly advisable to dehydrate the tar as
much as possible for any one of its applications, and in some cases it
is previously boiled in order to remove its more volatile constituents.

No preparation whatever is needed if the tar is to be used as _fuel_,
either for heating the gas-retorts or for other purposes. Its
heating-value is equal to the same weight of best coal, but it is very
difficult to burn it completely without producing a great deal of
evil-smelling smoke. This drawback has been overcome by employing the
same means as have been found suitable for the combustion of the heavy
petroleum residues, called "masut," viz. converting the tar into a fine
spray by means of steam or compressed air. When the gas-maker cannot
conveniently or profitably dispose of his tar for other purposes, he
burns it by the above means under his retorts.

Several processes have also been patented for producing _illuminating
gas_ from tar, the most notable of which is the Dinsmore process. This
process has been adversely criticized by very competent gas-makers, and
no great success can be expected in this line.

Coal-tar is very much employed for painting wood, iron, brickwork, or
stone, as a preventive against the influence of weather or the far more
potent action of corrosive chemicals. This, of course, can be done only
where appearance is no object, for instance in chemical works, where all
kinds of erections and apparatus are protected by this cheap kind of
paint. Coal-tar should not be used for tarring the woodwork and ropes of
ships, a purpose for which only wood-tar has been found suitable.

One of the most considerable outlets for crude tar is in the manufacture
of _roofing-felt_. This industry was introduced in Germany upwards of a
hundred years ago, even before coal-tar was available, and has reached a
very large extension both in that country and in the United States,
where most of the gas-tar seems to be devoted to this purpose. In the
United Kingdom it is much less extensive. For this manufacture a
special fabric is made from pure woollen fibre, on rolls of about 3 ft.
width and of considerable length. The tar must be previously dehydrated,
and is preferably deprived of its more volatile portions by heating in a
st