BAKER HUGHES - Drilling Fluids Reference Manual

Baker Hughes Drilling Fluids
Graduation
mark
A. Bulb
pipette
B. Graduated
pipette
C. Burette
Figure 3-14
Pipettes and Burette Used in Chemical Analysis
A bulb pipette (Figure 3-14 A) is used to measure out a certain volume, such as 5 or 10 ml, with
far greater accuracy that a measuring cylinder. The pipette is dipped into the solution, which is
then sucked up into the upper stem to above the graduation.
After ensuring that there are no air bubbles trapped in the liquid, the level is then slowly dropped,
using a finger on the top of the pipette, until the bottom of the meniscus coincides exactly with
the graduation mark. The pipette is then removed from the liquid and the lower end wiped to
remove liquid on the outside. The volume of liquid inside the pipette is then transferred to the
required container by removing the finger at the top and letting the liquid drain out slowly. The
pipette should not be blown our, nor should the last drop be shaken from the tip as this will alter
the volume delivered.
Bulb pipettes should never be used for any volume other than the one stated on the pipettes. The
straight stem, or graduated pipettes (Figure 3-14 B), are usually calibrated to enable different
volumes to be delivered.
The burette (Figure 3-14 C), is like a graduated pipette with a tap at the bottom which controls the
release of liquid. A burette is used for titrations as follows:
With the tap closed, it is filled with the titrant. This is usually a standard solution which reacts
with the ion under test. After filling, the tap is opened briefly to fill the lower part of the burette.
The burette is then checked for air bubbles. If these exist they can usually be removed by gently
tapping the sides of the burette or by rotating it rapidly (but carefully) between the palms of the
hands.
Before starting the titration, the level of titrant is recorded. The titrant is then added carefully to a
known volume of filtrate (added by pipette to the titrating flask) until the end point is reached.
The volume of titrant in the burette at the end point is then recorded and the volume used is
simply the difference between this reading and initial one.
The volume must never be allowed to drop below the last graduation mark or inaccurate readings
will be obtained. If the end point has not been reached with the burette nearly empty, the titration
is stopped, the volume is recorded and more titrant added to the burette with the new volume
recorded as before.
Baker Hughes Drilling Fluids
Reference Manual
Revised 2006 3-27