or sealing ring. Solid samples (up to 2 grams) can be
weighed directly into this dish before it is attached
to the bell. Liquid samples (up to 20 mL) can be added
to the closed cell from a pipet inserted through the
top stem.
To start the reaction, a glass push rod is inserted
from the top of the calorimeter through the stirring shaft
and into a socket in the sample dish. When this rod is
pushed downward, the dish slides out of the cell and
remains attached to the rod, held at a fixed distance
above the bottom of the reaction vessel. In this posi-
tion the rod and dish rotate with the cell, slinging the
reactants into the solution and serving as an additional
impeller in the stirring system.
Heat leak from the cell to the non-wetted parts of
the system is held to a minimum by a low conductivity,
thin walled glass stem on the sample cell and a plastic
coupling which fastens the cell to the stirring shaft. The
cell is easy to load, easy to clean and, if broken, it can
be replaced at minimum expense since the sample dish
and other parts are interchangeable. The dish itself is
made of Teflon reinforced with glass fiber for excellent
resistance to most chemical agents and good dimen-
sional stability.
The Stirrer Drive
The stirring mechanism consists of an externally
mounted electric motor with a drive belt which turns
the stirring shaft at a constant speed (approx. 450 rpm)
with no slippage and very little bearing friction. The
hollow drive shaft terminates at the underside of the
calorimeter cover where it joins the low conductivity
coupling on the end of the sample cell.
Easy to Operate
The operation of the 6755 Calorimeter is quite simple.
At the start of a test, one liquid is held in the glass
Dewar while the other reactant, either solid or liquid,
is held in the sealed rotating cell which is immersed in
the first liquid. The system comes to equilibrium quickly
with only a slight temperature drift from the heat of
stirring and from any heat leak into or out of the calo-
rimeter. After recording the initial drift and without inter-
rupting the rotation of the sample cell, the operator starts
the reaction by depressing the push rods which drop the
content of the cell into surrounding liquid. The reaction
then proceeds to completion under the vigorous stirring
action of the rotating cell.
Precision Thermometry
Temperatures in the Dewar are measured with a Parr
6772 Calorimetric Thermometer (described in detail on
page 3) which is included with the 6755 Calorimeter.
Readings are taken with a thermistor sealed in a stain-
less steel probe. Although the thermometry section
has a working range from10° to 50 °C, best calorimet-
ric results are obtained when working within +/- 5 °C
of room temperature, since the system depends on a
glass Dewar for controlling the heat leak.
The thermometer in the calorimeter can also be
used for general purpose, high precision temperature
measurement in other apparatus, using a thermistor
probe in a stainless steel sheath for measurements in
the 10° to 50 °C range.
Data Collection and Display
The 6755 Calorimeter has digital data outputs, as
well as an onboard data logging capability which will
store data in the instrument for later transfer to a com-
puter or to a printer.
The software built into the calorimeter can provide
temperature rise data which has been corrected for
heat leaks and the heat of stirring in the system or,
it can provide uncorrected temperature readings for
manual, computer or graphical analysis.
A Parr 1758 Printer is offered for users who wish to
take full advantage of the onboard calculation capabili-
ties of the calorimeter. This is a compact, 40-column
printer which will produce a printed record of all calori-
metric data when called up by the user. A standard USB
port with full configuration software is provided for the
printer connection. Users who already have a compa-
rable printer can use it with this connection.
Computers can also be connected to the Ethernet
communications port. This option will be attractive to
those who wish to use spreadsheets to write their own
data collection and reduction programs, or those who
wish to plot thermograms for graphical analysis. A fully
configurable charting program is provided for the calo-
rimeters LCD display.
Precision
The precision obtainable with the 6755 Solution
Calorimeter will be a function of the amount of heat
liberated by the reactants and the temperature at
which the test is conducted. The best precision will be
obtained when working with reactions which release
between 200 and 600 calories, producing a tempera-
ture rise of 1.5° to 5.0 °C at or near room temperature.
Under these conditions a standard deviation of less
than 0.4% of the determined value can be obtained in
repetitive tests. If the total heat release produces a
rise of less than 0.5 °C or more than 6.0 °C, or if the
test is conducted at higher working temperatures with
Model 6755 Solution Calorimeter
P a r r I n s t r u m e n t C o m p a n y
6
w w w . p a r r i n s t . c o m
