at different points and at various times during the charge.  The results of these experiments may be of some interest, and may lead to further investigation.  The temperatures were taken by mercurial thermometers registering 600 deg.  Fahr., except those near the mouthpiece, which were taken by a Siemens water pyrometer.  Every care was exercised to insure accuracy; and the instruments were carefully adjusted.  At a distance of 18 inches from the mouthpiece, the temperatures varied from an average of 890 deg., shortly after the retort was charged, to 518 deg. at the end of the charge; at 12 feet distant from the mouthpiece, the corresponding temperature was 444 deg., falling to 167 deg. at the end of the charge; and at 22 feet, the average temperature varied from 246 deg. at the commencement to 144 deg. at the end of the charge.  These are the averages of a number of experiments.  In some instances they were considerably above these averages—­temperatures over 900 deg. being frequently obtained.  This is about the temperature of a low red heat, and is much higher than any I have seen recorded.  When the gas was allowed to issue from a hole in the ascension pipe, 11/4 inches in diameter, 18 inches above the mouthpiece, a strip of lead held about an inch from the orifice was freely melted.

In the settings on which these experiments were made, the middle ascension pipe takes the gas from the two central retorts; and it is of interest to note that in this pipe the temperature of the gas 18 inches from the upper retort was found to be 1014 deg.  Fahr., and at the point where it entered the hydraulic main it was 440 deg.  Fahr.  Zinc was freely melted by the gas issuing from a hole 18 inches from the mouthpiece.  The temperatures always fall toward the end of the charge; the fall of temperature in the ascension pipe being a good indication that the charge is worked off.  They increase with the heat of the retort and with the weight of the charge.

Experiments were also made to ascertain the temperature of the gas in the retort; and for this purpose one of Murrie’s pyrometers was used, the action of which depends on the pressure produced by the vaporization of mercury in a malleable iron tube.  The end of this tube was first rested on the top of the coal, but not in contact with the retort.  It reached about 18 inches into the retort, and therefore was not in the hottest part.  In this position the temperature indicated shortly after charging the retort was 1110 deg.  Fahr., gradually rising to 1640 deg.  Fahr.  The end of the tube was then embedded in the coal, when the pyrometer indicated a temperature of 1260 deg.  Fahr. within 30 minutes after the retort was charged; gradually rising toward the end of the charge as before.  At the time these temperatures were taken, the retorts were each producing 10,000 cubic feet of gas per day.  I had no opportunity of testing the accuracy of the statement that, with lower temperatures, there is a tendency to stoppage of the ascension pipes; but with these high temperatures (contrary to what might be expected) there is no trouble from stoppages.