all the air had been expelled from the mercury, and no air would
gather in R_2 when it was lowered, the caustic potash was resorted to.
The reservoir R_2 was now again raised until the mercury in R_1 stood
above stopcock C_1. The caustic potash was fused and boiled, and the
moisture partly carried off by the pump and partly re-absorbed; and
this process of heating and cooling was repeated many times, and each
time, upon the moisture being absorbed or carried off, the reservoir
R_2 was for a long time raised and lowered. In this manner all the
moisture was carried off from the mercury, and both the reservoirs
were in proper condition to be used. The reservoir R_2 was then again
raised to the top, and the pump was kept working for a long time. When
the highest vacuum obtainable with the pump had been reached the
potash bulb was usually wrapped with cotton which was sprinkled with
ether so as to keep the potash at a very low temperature, then the
reservoir R_2 was lowered, and upon reservoir R_1 being emptied the
receiver r was quickly sealed up.

When a new bulb was put on, the mercury was always raised above
stopcock C_1 which was closed, so as to always keep the mercury and
both the reservoirs in fine condition, and the mercury was never
withdrawn from R_1 except when the pump had reached the highest degree
of exhaustion. It is necessary to observe this rule if it is desired
to use the apparatus to advantage.

By means of this arrangement I was able to proceed very quickly, and
when the apparatus was in perfect order it was possible to reach the
phosphorescent stage in a small bulb in less than 15 minutes, which is
certainly very quick work for a small laboratory arrangement requiring
all in all about 100 pounds of mercury. With ordinary small bulbs the
ratio of the capacity of the pump, receiver, and connections, and that