Temperature is a state of heat or coldness within a substance which can be measured against a standard scale. The instrument used for the measurement of temperature is the thermometer, which work on the principle that substances expand on heating and contract on cooling.
The standard scales most commonly in use are the centigrade and the fahrenheit scales. The fahrenheit scale was in common use but now there is general change over to centigrade. To convert the normal body temperature of 37 degree centigrade to fahrenheit, you will multiply 37 by 9/5 and add 32.
that is (37×9/5)+32=98.6
Then to convert a fahrenheit temperature to a centigrsde temperature, you will subtract 32 by 98.6 and multiply by 9/5.
that is (98.6-32)x5/9=37
Mercury is the material which is most commonly used in thermometers and has several advantages over other substances.
CHARACTERISTICS OF A MERCURY THERMOMETER
- It is a good conductor of heat and so rapidly reaches the temperature of the substance under rest.
- It is opaque and its level can easily be read when it is inside a transparent glass tube.
- It has a high boiling point and a low freezing point.
The thermometer is made from a piece of capillary glass tube which ends in an elongated bulb. The bulb is filled with mercury and heated so that all the air is driven out of the capillary tube. The upper end is then passed through a flame and sealed off. On cooling to room temperature, the mercury level drops leaving a vaccum above it. A protective glass covering, marked with a scale, is arranged round the capillary tube containing the mercury.
TYPES OF THERMOMETERS
This type of thermometer has been introduced to take the temperature of the patient’s bath water. It has been arranged so that it can scoop up a small quantity of bath water out of the bath to maintain the mercury at its correct level until the nurse can read the temperature. The scale on this thermometer usually ranges from -1 degree to 65.5 degrees centigrade.
This type of thermometer is used for taking the temperature of lotion used in various nursing treatments. The range in this case may vary. For instance -19 degrees centigrade to 115 degrees centigrade (0 degree F to 240 degree F), -6.6 degrees centigrade to 104 degrees centigrade (20 degrees F to 220 degrees F). This kind of thermometer will only give an accurate reading while held in the lotion.
In this case, the thermometer is used to register the atmospheric temperature in the hospital wards. Sometimes alcohol, coloured with red dye is used instead of mercury.
These thermometers are being used in some hospitals and special departments. The temperature is recorded rapidly and an accurate reading can be taken in either Fahrenheit or Centigrade scales. Different types are available, one for oral temperatures and a more sensitive type for recording skin temperature.
This thermometer is used to take the patient’s temperature and differs from the others. In that, it is self registering. There is a small kink in the bore of the capillary tube, just above the bulb,which the mercury will not run unless the thermometer is shaken. This self registering function is one of the considerable importance, the nurse may read and record the temperature in a suitable light after removing the thermometers usually extends from 35 degrees centigrade to 43 degrees centigrade (95 degrees F to 110 degrees F), and the length of time taken to register may vary from a half to three minutes, the optimum time being stated on the thermometer. When the temperature is being taken in the rectum, a special thermometer with a shorter, thicker, coloured bulb is used.