is different in various places
and for various objects. It depends upon the fact whether _soft_ or
_hard_ pitch is wanted. The latter must be made where it has to be
sold at a distance, as soft pitch cannot be easily carried during the
warmer season in railway trucks and not at all in ships, where it
would run into a single lump. Hard pitch is also always made where as
much anthracene as possible is to be obtained. For hard pitch the
distillation is carried on as far as practicable without causing the
residue in the still to "coke." The end cannot be judged by the
thermometer, but by the appearance and quantity of the distillate and
its specific gravity. If carried too far, not merely is coke formed,
but the pitch is porous and almost useless, and the anthracene oil is
contaminated with high-boiling hydrocarbons which may render it almost
worthless as well. Hard pitch proper should soften at 100 deg. C., or
little above.

Where the distillation is to stop at soft pitch it is, of course, not
carried up to the same point, but wherever the pitch can be disposed
of during the colder season or without a long carriage, even the hard
pitch is preferably softened within the still by pumping back a
sufficient quantity of heavy oil, previously deprived of anthracene.
This makes it much easier to discharge the still. When the contents
consist of soft pitch they are run off without much trouble, but hard
pitch not merely emits extremely pungent vapours, but is mostly at so
high a temperature that it takes fire in the air. Hard pitch must,
therefore, always be run into an iron or brick cooler where it cools
down out of contact with air, until it can be drawn out into the open
pots where its solidification is completed.

Most of the pitch is used for the manufacture of "briquettes" ("patent
fuel"), for which purpose it should soften between 55 deg. and 80 deg. C.
according to the requirements of the buyer. In Germany upwards of
50,000 tons are used annually in that industry; much of it is imported
from the United Kingdom, whence also France and Belgium are provided.
Apart from the softening point the pitch is all the more valued the
more constituents it contains which are soluble in xylene. The portion
insoluble in this is denoted as "fixed carbon." If the briquette
manufacturer has bought the pitch in the hard state he must himself
bring it down to the proper s