Time necessary for removal Greatest attainable
of half the air. exhaustion.
10 minutes 1 / 5,000,000
7.5 minutes 1 / 7,000,000
6.6 minutes 1 / 12,000,000
In point of fact the highest exhaustion I ever obtained with this pump
was 1 / 5,000,000; from which I infer that the leakage during action
is considerably greater than four times that of the pump at rest. The
general run of the experiments tends to show that the leakage of a plain
Sprengel pump, without stopcocks or grease, is, when in action, about 80
times as great as in the form used by me.
_Note on annealing glass tubes._--It is quite necessary to anneal all
those parts of the pump that are to be exposed to heat, otherwise they
soon crack. I found by inclosing the glass in heavy iron tubes and
exposing it for five hours to a temperature somewhat above that of
melting zinc, and then allowing an hour or two for the cooling process,
that the strong polarization figure which it displays in a polariscope
was completely removed, and hence the glass annealed. A common
gas-combustion furnace was used, the bends, etc, being suitably inclosed
in heavy metal and heated over a common ten-fold Bunsen burner. Thus far
no accident has happened to the annealed glass, even when cold drops of
mercury struck in rapid succession on portions heated considerably above
100° C.
I wish, in conclusion, to express my thanks to my assistant, Dr.
Ihlseng, for the labor he has expended in making the large number of
computations necessarily involved in work of this kind.--_Amer. Jour. of
Science._
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