with a modified form of Sprengel-pump. 101 
The mean value is gg7a4y-yy0; With a probable error of 
10°36 per cent of the quantity involve Upon other 
ceeaetrs I have tea exhaustions of be bcs anc 
aessivaos~ «6 f: course in these cases a gauge-correction was 
applied ; the highest vacuum that I have ever obtained irre- 
spective of a gauge-correction was yz gp-s$z75y_ In. these 
cases and in general, potash was employed as the dr ying ma- 
terial ; I have found it practical, however, to attain vacua as 
high as 50-v00a00 10 the total absence of all such substances. 
The vapor of water which collects in bends must be removed 
from hee to time with a Bunsen-burner while the pump is in 
actio 
Tei is evident that the final condition of the pump is reached 
when as much air leaks in per unit of time as can be removed in 
the same interval. The total average leakage per ten minutes 
in the pump used by me, when at rest, was ‘000211 cubic mil- 
aw tie at press. 760™. Let us assume ren em leakage when 
€ pump is in action is four times as gre s when at rest ; 
thee in each ten minutes ‘000844 mabe: Hannon press. 
760™ would enter; this corresponds in the pump used by me 
to an exhaustion - of Veraheae if the rate of the pump is 
such as to remove one-half of the air present in ten minutes, 
then the highest attainable exhaustion would be gzg-gta-w00- 
n the same way it may be shown that if six minutes are re- 
ee obtained with a plain i ihe -pump.—I made a 
series of experiments with a plain Sprengel- -pump without 
stopeocks, and arranged, as far as possible, like the instrument 
just described. The leakage per hour was as follows: 
Duration of the Leakage per hour in sobic 
experinient. mm. at press. 760 
a2 bout... a. “104868 
S GBYS oe sn eae ia wes 04520 
2 GBYR «365. 6. ORR1D 
4 GBYS - os ek, Ueeee 
Mean? 66503000). O88 
Chea the same reasoning as above we obtain the following 
e: 
