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CT-500 Instruction Manual
Isopropyl Alcohol
Isopropyl alcohol is less toxic than methyl alcohol and somewhat less volatile. However, it becomes
very viscous at low temperatures and is therefore unsuitable for use at very low temperatures.
Silicone Fluids
Silicone fluids are available in a wide range of viscosities and can be used over a wide range of
temperatures if the proper selection of viscosity is made for the temperature range of interest.
Silicones are also relatively expensive liquids. However, a bath containing silicones requires extra
care when used for capillary viscometry. If silicones are introduced into a viscometer capillary, its
calibration factor will be altered by a significant amount.
Water
Water is the ideal fluid in the temperature range in which it can be used. Because in some cases
there is a tendency for algae formation, a degree of water treatment may be necessary. Water can
be used at temperatures close to the boiling point, but water replenishment to offset evaporation
becomes a nuisance and the hot vapor can make working above the bath uncomfortable. Also, it
may be difficult to establish optimum control at elevated temperatures because of the rapid cooling
resulting from surface evaporation.
Refined White Oils
Refined white oils (paraffin oils) of relatively low viscosity can be used at temperatures above the
level at which water becomes unsatisfactory. Because these oils turn faintly yellow and continue to
darken with prolonged exposure to heat, CANNON recommends adding an oxidation inhibitor to
retard discoloration. The addition of an inhibitor prolongs the useful life of the oil, but it eventually
becomes as dark as untreated oil.
The search for more suitable bath oils is unending. Hydrogenated vegetable oils, coconut oil,
synthetic oils, and certain chemical compounds have been used with some success at various
temperatures.
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