an improved Air •'Pimp, &c. 
of elaftic fluid, or to receive into a bladder the elaflic fluid that 
is contained in the receiver. 1 hus, luppofe I want to intro- 
duce fome fixed air into the receiver ; firfl, I exhaufl the com- 
mon air from the receiver, then put the flop-cock of a bladder 
containing fixed air to the hole X ; laflly I open the flop-cock 
of the bladder, and turn the cocks tiZ , fo tiiat their fide-holes 
may be turned towards X, and by working the pump the fixed 
air will immediately pafs from the bladder into the receiver. If 
now this fame fixed air is required to be introduced into a blad- 
der again, the flop-cocks mult be turned with their fide holes 
towards k , and a flop-cock with an empty bladder is put to the 
hole k; then, by working the pump, the fixed air will be gra- 
dually introduced from the receiver into the bladder. 
Having fm 1 (he cl the defenption of tins improved air-pump, 
which, befides its exhaufting much better, has various other 
advantages over any other inflrument of the kind ; I (hall con- 
clude this paper with the fuccinct account of fome experiments 
made with it, principally to determine how far it can rarefy 
the air. 
Experiments made with the above-deferibed air-pump . 
Previous to the narrative of the experiments, it is necefiary 
to mention, that both the plate, and the lower edges of the 
receivers of this pump, are ground fo perfectly true, as not to 
require any leathers, nor even oil ; however, for greater fecu- 
rity, fome oil is generally poured on the outfide of the edge of 
the receiver, after having exhaufted it a little ; and it is very 
ieldom, that any vifible quantity of this oil paflfes within the 
receiver, between its edge and the plate of the pump. 
Vol. LXXIII. N n n 
When 
