80° F. 70° F.
72 64
67 60
60 54
55 50
50 46
42 40
Say, for example, the room was at 57° and the water placed in the
cylinder was at 46°: add a little hot water and stir with the
thermometer until it assumes 52°. By the time the excess of water has
been removed with a pipette until it is exactly level with the mark, and
all is ready, the temperature will rise nearly 0.5°. Let the thermometer
be immersed in the water at least three minutes before reading. The fuse
should be placed in the mixture, and everything at hand before reading
and removing the thermometer. After igniting the fuse and immersing the
copper cylinder in the water, the apparatus should be kept in the best
position for the gases to be evolved all around the cylinder, and the
rate of combustion noted. Some coals are very unmanageable without
practice, and samples of "patent fuel" are sometimes met with,
containing unreasonable proportions of pitch, which require some caution
in working and very close packing, inasmuch as small explosions occur
during which a little of the fuel escapes combustion.
In order that the experiment shall succeed well, experience has shown
that the nature of the fuse employed has much to do with it. Plaited
or woven wick is not adapted, and will fail absolutely with dry coals,
unless it is made very free burning. In this case not less than
three-quarters of an inch in length is necessary, and the weight of such
is very appreciable. I always use Oxford cotton, and thoroughly soak it
in a moderately strong solution of nitrate of potash. When dry it should
burn a little too fast. The cotton is rubbed between two pieces of cloth
until it burns just freely enough; then four cotton strands are taken,
twisted together, and cut into lengths of ¾ inch and thoroughly dried.
Open out the fuse at the lower end when placing it in the mixture so as
to expose as much surface as possible in order to get a quick start, but
carefully avoid pressing the material, and use a wire to fill up close
to the fuse. A slow start often spoils the experiment, through the upper
end of the cylinder becoming nearly filled up with potassic chloride,
etc.
By paying attention to such details, and following the method
recommended, the apparatus yields very satisfactory results with
bituminous and semi-bituminous coals.--_Chemical News_.
* * * * *