These experiments, so far as they have gone, lead to the conclusion that the temperature of the gas as it is evolved from the coal is not less than 1200 deg.  Fahr., and that cooling commences immediately on the gas leaving the retort.  The temperatures being far above that of liquefaction, the gases are cooled very rapidly.  The temperature of the gas in the ascension pipe depends on the rapidity with which the gas is evolved—­that is to say, the greater the quantity produced in a given time, the less effective is the cooling action of the mouthpiece and the ascension pipe; and although I had no opportunity of testing it, I should expect to find that with retorts making from 5,000 to 6,000 cubic feet of gas per day, the maximum temperature in the ascension pipe 18 inches from the mouthpiece will not exceed 400 deg. to 500 deg.  Fahr., while with lower heats and lighter charges the temperatures will be still lower.  That these temperatures have some effect in causing or preventing stoppage in the ascension pipes there can be no doubt; and it is important that this subject should be thoroughly investigated.

It is of interest to consider what must be the physical condition of the gas at these high temperatures.  All the hydrocarbons which are afterward condensed must then be in the condition of gases having various degrees of condensability, mixed with and rendered visible by a cloud of carbon particles or soot.  If this soot could be removed from the gas at this stage without reducing the temperature, we should probably have no thick tar or pitch, but only comparatively light-colored oils; and it might possibly lead to an entirely different mode of conducting the process of condensation.

These are a few of the subjects on which it is extremely desirable that we should possess that complete information which can only be obtained by well-directed investigations with different materials and under varying conditions.  There are many others in connection with carbonization and purification which might be mentioned; but I think I have said sufficient to show the necessity that exists for more minute investigation and research.  Investigations such as are here indicated do not involve any large expenditure of money; but they do require care and intelligence to prevent errors being made.  Experiments should not be condemned as defective because the results differ from old-established theories; yet when this does happen, it is in all cases better to suspect the new experiment rather than the old theory, until the results have been fully established.—­Wm. Foulis, Journal of Gas Lighting.

* * * * *

THE LARGEST BLACK ASH FURNACE IN THE WORLD.