Water Bath

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-A water bath is a device that maintains water at a constant temperature.
-It allows the heating of small amounts of fluids over a period of time without changing the concentration of constituents by evaporation.
-It is also used when several tubes are to be handled while maintaining the temperature of the contents,e.g., in coagulation tests.
-Water bath is an instrument used for maintaining a uniform temperature throughout the fluid contained in a glass container by keeping it in pre–heated water.
-It also prevents excessive evaporation of the fluid being heated.
Components
-It is made up of insulated metal, usually stainless steel or of heat resistant glass with or without an insulated lid.
-An electric element to heat the water contained in the trough.
-A propeller or stirrer to circulate the water in the trough in order to maintain a uniform temperature throughout the trough.
-A thermometer to check the temperature. This may be in-built or placed separately in the trough.
-A thermostat to maintain the temperature at a constant level.
Water Bath Controls
-Temperature Control :
All water baths have a control to set temperature. This control can be digital or a dial. Often there is an indicator light associated with this control. When the light is on the water bath is heating. When the water bath reaches the set temperature, it will cycle on and off to maintain constant temperature.
-Safety control :
Most water baths have a second control called the safety. This control is set at the maximum temperature the water bath should attain.It is usually set just above the temperature control. Often an indicator light is associated with the safety control. If the water bath reaches the temperature that the safety control is set at, the light will go on. It will be impossible for the water bath to heat higher than the safety setting even when the temperature setting is higher.
-Shaking Control:
Shaking water baths have additional controls for shaking. The shaking mechanism can be turned on or off. The speed of shaking can also be set.
Operating procedure
-Fill it with clean (preferably distilled) water to a desired level and then switch it on.
-Set the thermostat to desired temperature and allow the water to warm to that temperature.
-Check the temperature from the thermometer.
Precautions and maintenance
-Clean from inside and change the water daily.
-This will prevent encrustation of stirrer, heat probe and thermostat with salts contained in raw water.
-It will also prevent the growth of fungi and algae.
-Keep the lid closed when not in use to prevent evaporation of water.
-Periodically check and counter-check the water temperature with internal as well as with an external thermometer.
-The thermometer should be placed in such a way that it is away from the heating element and the walls.
Specifications of a water bath for district laboratories
-Unstirred with hydraulic thermostat or electronic temperature control.
-Operating over a temperature range from ambient to 60 °C or above.
-Having a 4 litre capacity.
-Fitted with a thermometer.
-Supplied with a lid.
Uses
-It provide Indirect heat.
-Used for warming blood bag blood.
-Used for incubation of test such as PT, APTT and Coombs test.