Page 124 - The Veterinary Laboratory and Field Manual 3rd Edition

The selection, use, maintenance and quality control of laboratory equipment and supplies 93

• When handling strong corrosive acids, and
similar, select volumetric ware manufactured
from chemically resistant borosilicate glass.
• Do not expose volumetric glassware to direct
heat, for example, hotplates, Bunsen flame.

Volumetric glassware is available in two accuracy
classes:

• class A/AS:

• highest measurement accuracy
• class AS has the same high tolerances as
class A, but is designed to permit more
rapid outflow on burettes and pipettes

• class B:

• approximately half of the measurement
accuracy of class A/AS.

Figure 2.58 Measuring volumes, reading the
Working with volumetric instruments meniscus. The volume has to be read at the low-
est point of the liquid level. The lowest point of the
meniscus has to touch the upper edge of the grad-
Always try to avoid significant temperature dif-
ference between the measuring instrument and uation mark. Photo: Willy Schauwers, Provincial
the liquid. Institute for Hygiene, Antwerp, Belgium.

Reading the meniscus Bottles

The volumetric instrument is held upright and Reagent bottles are available in a variety of sizes
the observer’s eye must be at the same height as and types. Plastic bottles should only be used
the meniscus. In this position, the ring mark will for reagents that do not interact with plastic.
appear as a line. The meniscus will appear darker The bottle size should not be much larger than
and more easily readable in front of a light back- the volume of reagent to be used. Brown bottles,
ground if a piece of dark paper is held behind the glass and plastic, are available for storage of light
instrument immediately beneath the ring mark sensitive reagents. The borosilicate reagent bot-
or graduation mark (Figure 2.58). The volume tles with a blue pouring ring and screw cap (both
has to be read at the lowest point of the liquid polypropylene) are very convenient for most lab-
level. The lowest point of the meniscus has to oratory use (Figure 2.59). They are available in
touch the upper edge of the graduation mark. amber glass as well.

Vet Lab.indb 93 26/03/2019 10:25