Mercury and Alcohol Glass Thermometers

By Joan Whetzel

Glass thermometers are not used so much these days, having been taken over by their more efficient electronic counterparts. They are, however, still around for some uses like cooking and lab work. Both alcohol and mercury have been used in the thermometers’ center tube to indicate the temperature of the person, thing, or liquid being measured. They come in a wide variety of temperature ranges, including Fahrenheit (F), Celsius (C) and Kelvin (K). Temperatures measured by glass thermometers run from the lowest temperature of 700Kelvin to the highest at 10000Celcius. The most common temperature range for glass thermometers fall between -400C to 2500C (-400F to 4820F).

Advantages and Disadvantages of Glass Thermometers

Glass thermometers have many advantages. 1. They’re easily portable and don’t take up much space,. 2. They don’t require auxiliary equipment (computer hookup to record the data).

3. They’re cheap. 4. They fit into just about any environment or setting. 5. They’re fairly sturdy. Glass thermometers also have some disadvantages. 1. It’s not possible to get continuous temperature readouts as with digital thermometers. 2. They don’t show changes over long time periods, which means temperatures have to be manually checked frequently. 3. Glass is breakable, creating the opportunity for injuries to the user. 4. Because they aren’t connected to a computer, the temperatures must be written down, which causes a time delay in recording the data.

Thermometer Construction

Both mercury and alcohol glass thermometers consist of several parts. The main parts include the following.

1)      Bulb: This is the reservoir that contains most of the alcohol or mercury.

2)      Stem:   The stem is the long, thin glass tube, making up the body of the thermometer.

3)      Capillary: the hollowed out bore in the center of the stem in which the mercury or alcohol rises when exposed to heat. To return the fluid to the bulb, the thermometer must be held at the top end and shaken.

4)      Main Scale: The engraved, etched hash marks – or graduation lines – that indicate the temperature reading based on where the fluid inside the capillary stops rising. There may be a colored backing to help make the mercury or red colored alcohol more visible and easier to read.

Alcohol Vs. Mercury Thermometers

The liquid inside glass thermometers usually comes in two types: mercury, which is silver in color, and alcohol which is dyed red to make it more visible. Mercury thermometers are the most reliable for temperature readings, but they have one major drawback. The mercury is toxic to humans and animals. Mercury thermometers haven’t been made for decades due to the poisonous nature of the metal, and it is recommended that if you have one, that it should be disposed of in order to remove the possibility of mercury poisoning. They should not be simply thrown away in the trash due to the potential for mercury poisoning. If you still have one of these at home, check with local pharmacies or law enforcement agencies to find out the best way disposing of them. If the thermometer breaks, collect all of the mercury and broken glass in a sealable container – being careful not to touch it with your hands. Then dispose of properly.

Nowadays, glass thermometers contain organic liquids such as alcohol, toluene, pentene, and butane. The thermometers for home use contain alcohol, dyed red to make them easier to read.

How Thermometers Work

Alcohol is also used in scientific thermometers that require temperatures below the freezing point of water. Alcohol has a freezing point of -1120C (-169.60F) which much lower than that of mercury, which freezes at 380F (30C). The bulb of the thermometer is exposed to the object, person or liquid whose temperature needs measuring. The fluid in the bulb expands when heated, causing the fluid to rise inside the capillary. When the fluid inside the bulb is cooled, it contracts and falls down the capillary and into the bulb. The temperatures are then read by comparing the

One Other Problem with Alcohol and Mercury Thermometers

One problem with both mercury and alcohol thermometers is that the fluids can become separated inside the capillary. This can then lead to inaccurate readings unless the mercury or alcohol is remixed by some method like centrifuging or shaking