better are the results. In two retorts of the same size, one making
5,000 and the other 10,000 cubic feet per day, the gas will be twice
as long in contact with the surface of the retort in the former as in
the latter--to the probable detriment of its quality, and increased
tendency to stoppage in the ascension pipes.

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° to 300°
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° 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