and other Parts of India. Ib 
fphere acting on the furface of the pifton attached to the arm 
of the balance, it is made to defeend, and to raife the other 
arm that is fixed to the pump; while this, being fomewhat 
heavier, immediately finks again, which carries up the pif- 
ton, while the cylinder is again filled; and thus, by alter- 
nately cooling and filling it, is the machine kept in motion ; 
the power exerted in raifing the pump-arm being always in 
proportion to the diaweter of the cylinder, or to the furface 
of the pifton, which is cxaétly fitted to it, and on which the 
preffure acts. 
The contrivance, too, of having the under part of the 
alembic, where the condenfed vapour is collected, or upper 
part of what they call the adkwr, of earthen-ware, of fo great 
a-thicknefs, and of courfe at fo great a diftance from the heat 
in the body of the fiill, is well imagined to keep the fpirits 
the cooleft poffible, when colleSted, and running off. 
By thus cooling and condenfing the vapour, likewife, fo 
fuddenly as it rifes, there is, in a great meafure, a conftant 
yacuum made, or as much as poffible can be; but, that both 
fleam rifes fafter, and that water boils with much lefs heat 
when the preflure is taken away from its furface, is an axiom 
in chemiftry too well known to need any iluftration ; it 
boiling in vacuum when the heat is only uinety or ninety- 
five by Farenheit’s thermometer; whereas in the open air, 
under the preflure of the atmofphere, it requires no lefs than 
that of two hundred and twelve, ere it can be brought to the 
boiling point. 
I muf further obferve, that the fuperior excellence of con- 
denfing the vapour fo effeCtually and {peedily in the alembic 
to our method of doing it in a worm and cooler, is greatly 
on the fide of the former; both from the reafons I have al- 
ready adduced, and becaufe of the {mall fiream of vapour 
that can be only forced into the worm, where it is condenfed 
gradually as it defcends ; but, above all, from the nature of 
yapour itfelf, with refpect to the heat contained in it, which 
of late has been proved, by the very ingenious Doctor Black, 
to be greater by far than, before his difcoveries, was ima- 
ined. For vapour he has fhewn to be in the fate of a new 
“fluid, where water is diffolved by heat; with the aififiance, 
9 Cz perhaps, 
