Drop / Bubble Counter
6
If accuracy is not critical and you are using the reagent reservoir and tip supplied with a low
viscosity liquid (like water) and the flow rate set to: -
Fast e.g.
10 plus
drops per second, use the
24
drops/cm
3
range.
Medium e.g. between
5
– 10
drops per second, use the
25
drops/cm
3
range.
Slow e.g. between
1.5
– 5
drops per second, use the
26
drops/cm
3
range.
Very Slow e.g.
less than
1.5
drops per second, use the
27
drops/cm
3
range
Note: When used with a pH or Conductivity Sensor, the flow rate needs to be very slow (less
than 1.5 drops per second) to allow the Sensor time to settle to a new reading after addition of
the titrant.
To calculate the number of drops in a cm
3
The volume of a drop of fluid (and therefore the number of drops per cm3) depends on a
number of factors. These include the:
Size and shape of the dropper end
Type of solution (its density, viscosity and surface tension)
Flow rate of the liquid through the dropper end (the slower the dropping the smaller the drop)
1. Set up the reagent reservoir in the alignment adapter of the Counter. Close both
stopcocks (a) and fill the reservoir with the solution being used.
2. The first step is to adjust the flow rate. Place a beaker under the stopcock to catch the
drops. Fully open the lower stopcock (b). Slowly turn the top stopcock (c) until it begins to
produce drops and then finely adjust the drop rate. When the correct flow rate of drops is
achieved close the lower stopcock (d) to stop the flow. Now the ‘flow rate’ is set, do not
adjust the top stopcock
– leave in this position. Use the lower stopcock to turn the drops
on and off (e).
Note: Do not set the flow rate too fast or the drops may form a stream and will not be counted as
individual drops.
3. Top up the reservoir. Place the accurate measuring container e.g. volumetric flask (10
mls or less) under the dropping tip.
4. Set the range of the Counter to Drop/Bubble (Count). Press the zero reset button.
5. Open the lower stopcock
fully
and count the number of drops required to fill up to the
volume mark on the measuring container. Use the lower stopcock to turn the drops off.
Notes: Make sure the lower stopcock is fully open or the rate of flow (and therefore the number of
drops per cm
3
) will be affected.
Closed
(OFF)
Open
(ON)
Closed
(OFF)
Closed
(OFF)
Closed
(OFF)
Open
(ON)
Open
(ON)
Open
slowly to
adjust
drop rate
Partly
Open
Partly
Open
(e)
(d)
(c)
(b)
(a)
