252 Mr. Pepys’ Account of a new Eudiometer’. 
measure being brought to the level of that in the cistern, the 
quantity of absorption is then to be determined, which is done 
as follows : 
Suppose atmospheric air has been the subject of the experi- 
ment, and consequently a large residuum left : first note the 
hundred parts ; and then to obtain a knowledge of the frac- 
tional parts, remove the measure into the small cistern, in 
which the graduated tube filled with mercury is placed : slide 
the tube above the surface of the fluid in the measure, and 
opening the stop-cock, suffer the mercury to descend till it has 
drawn the fluid in the measure to a regular division ; then 
stop the cock, and register the hundred parts on the measure, 
and the thousand parts on the graduated tube ; the united 
quantities give the sum of the residual gas. Observe well in 
registering the thousand parts, that the fluids are exactly on a 
level, on the outside and the inside of the measure ; this may 
be easily effected, by pouring out a portion of the liquid of the 
small cistern, or adding thereto. 
If instead of atmospheric air, a gas is tried, which so far as 
it is uncontaminated can be nearly wholly absorbed by the 
reagents employed, the process becomes exceedingly simple; 
for if the residuum is under a hundred part of the measure, 
it may be transferred completely into the graduated tube, and 
its quantity at once ascertained. 
The stopper S would have injected the fluid with greater 
velocity had it been straight, but it would not then have been 
so convenient in the analysis of compound gases, where both 
mercury and hot solutions are occasionally employed, as the 
mercury would have so compressed the fluid in the bottle, in 
