54 
CHEMISTRY: RICHARDS AND DAVIS 
ference can only be accounted for by differences in the time actually 
required for the burning of the substances in the bomb. This con- 
clusion is entirely in accord with that of Benedict and Fletcher,^ based 
upon the measurement of the pressures developed during the com- 
bustion of solid substances. 
The immediate practical problem was to match this rise in the calorim- 
eter by an equal rise in the environment. 
Since the rise in temperature of the calori- 
metric environment, caused by adding sul- 
phuric acid to the alkaline outside bath, 
is directly proportional to the amount of 
acid added, a device was needed for de- 
livering very little acid at first, then rapid- 
ly increasing the amount, then for some 
time adding acid at a nearly constant rate, 
and finally diminishing the stream until it 
is reduced to nothing, in order to follow 
the carefully ascertained course of the rise 
of temperature of the calorimeter. These 
differences in rate of flow can easily be at- 
tained by constructing an apparatus for 
delivering acid automatically under differ- 
ent pressures. To attain the first part of 
the curve the level of the acid must run 
uphill; to parallel the straight line during 
the rapid rise, the liquid must be delivqred 
from a larger reservoir of nearly constant 
level; to match the last part of the curve, 
it must rapidly sink in a fine delivery 
tube. The necessary dimensions of the 
several tubes were found by trial, and an 
apparatus like that shown in figure 3 was 
found to serve the purpose excellently. 
The tube to the right hand had to be long and spiral because its inside 
diameter could not be greater than 4 mm., on account of the small 
capillary constant of concentrated sulphuric acid. 
For each substance with each method one or two preliminary trials 
determined the general inclination of the curve. Previous experiments 
with alterations in the stopcock showed the inclination corresponding 
to each position on its scale. Therefore, for any particular substance, 
when all was ready for the combustion, the stopcock E had simply to 
FIG. 3 
A, stopcock for admitting sul- 
phuric acid to apparatus in pro- 
cess of filling, N being open; M, 
stopcock for starting and stopping 
flow of acid into tank; E, regulat- 
ing stopcock for determining rate 
of flow without altering general 
character of curve. 
