(a) Mixing Water Samples.
The following two methods may be
helpful in tests where it is necessary to mix the water sample with
chemicals (usually indicated by the instructions, Swirl to mix).
When mixing is done in a square sample cell, the
swirling motion is attained by a simple twisting motion as shown in
This is done by grasping the neck of the cell with the
thumb and index finger of one hand while resting the concave bottom of
the cell on the tip of the index finger on the other hand.
cell quickly, first one way and then the other, to mix the samples.
A swirling motion is also recommended when the mixing
takes place in a graduated cylinder or a titration flask.
case, however, grip the cylinder (or flask) firmly with the tips of
three fingers (fig. 2-1).
Hold the cylinder at a 45 degree angle and
twist the wrist.
This motion will move the cylinder in an approxi-
mately 12-inch circle, thereby giving liquids an intense rotation
which accomplished complete mixing in a few turns.
(b) Reading the Meniscus.
When small sample quantities are
used, the accuracy of the measurements is very important.
illustrates the proper way of reading the sample level or the
meniscus formed when the liquid wets the cylinder or pipet walls.
Never pipet chemical solutions or unknown water
samples by mouth.