164. *Q.*—Have not many plans been
already contrived which consume the smoke of furnaces
very effectually?

*A.*—Yes, many plans; and besides
those already mentioned there are Hall’s, Coupland’s,
Godson’s, Robinson’s, Stevens’s,
Hazeldine’s, Indie’s, Bristow and Attwood’s,
and a great number of others. One plan, which
promises well, consists in making the flame descend
through the fire bars, and the fire bars are formed
of tubes set on an incline and filled with water,
which water will circulate with a rapidity proportionate
to the intensity of the heat. After all, however,
the best remedy for smoke appears to consist in removing
from it those portions which form the smoke before
the coal is brought into use. Many valuable products
may be got from the coal by subjecting it to this
treatment; and the residuum will be more valuable
than before for the production of steam.

165. *Q.*—Have experiments been made
to determine the elasticity of steam at different
temperatures?

*A.*—Yes; very careful experiments.
The following rule expresses the results obtained
by Mr. Southern:—To the given temperature
in degrees of Fahrenheit add 51.3 degrees; from the
logarithm of the sum, subtract the logarithm of 135.767,
which is 2.1327940; multiply the remainder by 5.13,
and to the natural number answering to the sum, add
the constant fraction .1, which will give the elastic
force in inches of mercury. If the elastic force
be known, and it is wanted to determine the corresponding
temperature, the rule must be modified thus:—From
the elastic force, in inches of mercury, subtract
the decimal .1, divide the logarithm of the remainder
by 5.13, and to the quotient add the logarithm 2.1327940;
find the natural number answering to the sum, and
subtract therefrom the constant 51.3; the remainder
will be the temperature sought. The French Academy,
and the Franklin Institute, have repeated Mr. Southern’s
experiments on a larger scale; the results obtained
by them are not widely different, and are perhaps
nearer the truth, but Mr. Southern’s results
are generally adopted by engineers, as sufficiently
accurate for practical purposes.