1/128,834,063 ......Feb. 1.
1/226,757,400 ..... Feb. 9.
1/232,828,800 ..... Feb. 19.
1/388,200,000 ......March 7.
That this diminution is not due to the air being gradually withdrawn
from the walls of the gauge or from the gauge-tube, is shown by the fact
that during its progress the pump was several times taken to pieces, and
the portions in question exposed to the atmosphere without affecting
the nature or extent of the change that was going on. I also made one
experiment which proves that the gauge-correction does not increase
sensibly, when the exhausted pump and gauge are allowed to stand unused
for twenty days.
_Rate of the pump's work_.--It is quite important to know the rate of
the pump at different degrees of exhaustion, for the purpose of enabling
the experimenter to produce a definite exhaustion with facility; also if
its maximum rate is known and the minimum rate of leakage, it becomes
possible to calculate the highest vacuum attainable with the instrument.
Examples are given in the tables below; the total capacity was about
100,000 cubic mm.
Time. Exhaustion. Ratio.
1/78,511
10 minutes }........ 1:1/3.53
1/276,980
10 minutes }........ 1:1/6.10
1/1,687,140
10 minutes }........ 1:1/4.15
1/7,002,000
Upon another occasion the following rates and exhaustions were obtained:
Time. Exhaustion. Rate.
1/7,812,500
10 minutes }........ 1:1/3.18
1/24,875,620
10 minutes }........ 1:1/2.69
1/67,024,090
10 minutes }........ 1:1/1.22
1/81,760,810
10 minutes }........ 1:1.67
1/136,986,300
10 minutes }........ 1:1.23
1/170,648,500
The _irregular_ variations in the rates are due to the mode in which the
flow of the mercury was in each case regulated.
_Leakage_.--We come now to one of the most important elements in the
production of high vacua. After the air is detached from the walls of
the pump the leakage becomes and remains nearly constant. I give below a
table of leakages, the pump being in each case in a condition suitable
for the production of a very high vacuum:
Duration of the Leakage per hour in
experiment cubic mm., press.,
760 mm.
18½ hours............................ 0.000853
27 hours............................ 0.001565
26½ hours.............................0.000791
20 hours.............................0.000842
19 hours.............................0.000951
19 hours.............................0.001857
7 days..............................0.001700
7 days..............................0.001574