A subject closely allied to that just alluded to is the temperature of the gas as it leaves the retort. Until within the last few years, it was generally assumed that this was not higher than from 200 deg. to 300 deg. Fahr.; and a very plausible theory was given to account for such a comparatively low temperature. A discussion which took place a few years ago in the _Journal of Gas Lighting_ showed that at that time opinions on this subject were not unanimous. But the conclusion arrived at seemed to be that the gas was not higher in temperature than that before stated; and if higher temperatures were observed, they were due to the tarry matter in the gas, and were not those of the gas itself. A little reflection is sufficient to show that the existence of gas intimately mixed with tarry matter at a high temperature, without being itself raised to that temperature, is a physical impossibility. In a paper read to a Continental gas association about a year ago, the writer stated, as the result of many experiments, that unless the temperature in the ascension pipe rises above 480 deg. Fahr., thickening of the tar in the hydraulic main and choking of the ascension pipe will certainly occur. This led me to make a series of experiments, extending over many months, on the temperature of the gas in the ascension pipes 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.