Page 105 - The Veterinary Laboratory and Field Manual 3rd Edition

74 Willy Schauwers

baths available, some made of plastic or glass (to dissolved salts and gases, and it should have low
allow observation). Most are made of a corrosion electrical conductivity. It is essential that there is
resistant metal, heated by an element and ther- always a supply of stored pure water available.
mostatically controlled. A propeller may be used For laboratory use, water is usually stored in 5
to distribute heated water evenly around the bath or 10 l containers made of good quality glass or
to maintain a set temperature. A thermometer polyethylene with screw cap and stopcock.
(digital or analogue) is usually supplied with the Water should not be stored for too long
bath. The temperature of a digital read-out water before use and the containers should be cleaned
bath or thermometer should be recorded daily regularly and checked visually for the presence
(see ‘FORM-SOP-LABORATORY-EQUIP-05–02 of contaminants. Good quality water can be pro-
Temperature registration thermometer’). Rotating duced using either deionizers or distillers and
or shaking water baths may also be used for some maybe a combination of both (Figures 2.38 and
laboratory procedures but these are usually more 2.39).
expensive. Simple shelves or storage packs can be
purchased for holding specimens in most types of Distillers
water bath.
All distillers (stills) work on the principle that
impure water is boiled and the resultant steam
Use and maintenance
is passed over a cold surface where condensate
• Do not use a lid when open vessels are in the is collected. This condensate is pure, or almost
bath because condensate drips may contami- pure, water. The cold surface is maintained by
nate the vessel contents. running water and a distiller can use a lot of tap
• Water and electricity together are dangerous water in a working day. It is therefore impor-
so regularly check electrical connections for tant that this residual water is utilized either for
signs of wear. washing glassware, since it is warm, or that it is
• Make sure that the water has reached the diverted to a storage tank.
required temperature before starting incuba- Stills are basically of two types, the long estab-
tion and that the water level in the bath is lished ‘Manesty’ still, which is made primarily
6
over the level of the incubating liquids. of stainless steel (wall mounted), and glass dis-
• The water in the bath should be deionized, tillers (like GFL water stills) which are usually
distilled, boiled or rain water and the recom- bench based models. The SOP for the ‘Manesty’
mended level maintained. distiller can be found in ‘SOP-LABORATORY-
• Clean the water bath regularly, do not dam- EQUIP-08 Distiller’.
age the heating element. If scale is present: There are advantages and disadvantages to
add some concentrated acetic acid, heat up each type of still. When deciding which model
the water bath and leave the acid solution for is the right one, it is necessary to consider the
a few hours until the scale is dissolved. relative robustness of the models, the price, run-
ning costs, and the quality and quantity of water
produced. It is important that the model selected
Water distillers and deionizers
has automatic electricity cut out switch in case
Good quality water is essential in a laboratory of overheating. This may occur as a result of
for many tasks including preparation of reagents, power fluctuations or water supply failure. The
solutions and media and for rinsing clean glass- cooling water supply often fluctuates so the tap
ware. Good quality water contains little or no should have two controls, one directly from the

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