How many degrees below which the thermometer drops

Everyone should prepare a thermometer at home. When you have fever symptoms, you can use the thermometer to measure your body temperature more conveniently. But everyone knows that if a thermometer is left for a long time, it will return to a normal temperature state. At this time, if you want to use it, you need to shake the thermometer twice. Many people don’t know how low the thermometer should be shaken to when using it. So how low should the thermometer be shaken to?

How many degrees should the thermometer be shaken to?

To measure body temperature, the thermometer needs to be shaken to below 35 degrees. If it is not swung below 35 degrees, the measured value will not be accurate. Why?

The thermometer relies on mercury to be affected by body temperature, and the degree of volume increase indicates body temperature. In order to facilitate reading, once the thermometer leaves the human body whose temperature is higher than the ambient temperature, the mercury will shrink in volume, causing the mercury column to break at the capillary expansion near the head, leaving a section of the mercury column to indicate the temperature (body temperature) that has been reached; when the thermometer is used again, if the temperature rises and the interrupted mercury column cannot be connected, there will be a hole in the mercury column and the temperature indication will be wrong.

Therefore, before using the thermometer, you should check whether the mercury inside can be "connected as a whole". If the original temperature indicated is high, shake it and use the centrifugal force to make the mercury remaining outside return to the head as much as possible. When you measure the temperature again, the mercury column can be connected as a whole. This is an accurate way to use a mercury thermometer. Because human body temperature is generally above 35 degrees Celsius when measured under the armpit, before measurement, the mercury column indicates below 35 degrees. Even if the under-arm measurement method is used, the expansion of mercury can connect the broken parts. Therefore, the standard for shaking is just below 35 degrees.

I just did a comparative experiment: I used an alcohol thermometer with a range of 100 degrees to measure the temperature of the water in a large thermos cup. When the water temperature was adjusted to 37 degrees, the same thermometer was shaken to different positions below 37 degrees before measurement, and then placed in 37-degree water. The reading was taken one minute later, which was basically 37 degrees. When the water temperature dropped to 36 degrees, the thermometer that originally indicated 37 degrees still read 37 degrees after being put in. Only when the thermometer was shaken to even more than 35 degrees and then placed in 36-degree water could a reading of 36 degrees be obtained. Therefore, before using the thermometer, shake the original temperature indication so that it indicates a temperature lower than the expected temperature (axillary temperature may be lower than 35 degrees in a cold environment, sublingual temperature and rectal temperature are less affected by the environment and will not be lower than 35 degrees). In actual measurement, the mercury column can continue to rise to body temperature, and the reading will not have a large error, that is, it can be shaken to less than 35 degrees (not to mention that it is not very accurate if it is shaken by hand).

What is a thermometer?

A clinical thermometer is a maximum thermometer that records the highest temperature ever measured by the thermometer. After use, the thermometer should be put back on the surface. That means holding the upper part of the thermometer and shaking it downward with force will make the mercury that has risen into the tube return to the glass bulb. Other thermometers must not be shaken, which is a major difference between clinical thermometers and other liquid thermometers.

A thermometer is also called a medical thermometer. The working substance of a thermometer is mercury. The volume of its glass bubble is much larger than that of the capillary tube above. The mercury in the bubble undergoes tiny changes due to the influence of body temperature. The expansion of the volume of the mercury causes a noticeable change in the length of the mercury column in the tube. Human body temperature generally fluctuates between 35℃ and 42℃, so the scale of a thermometer is usually 35℃ to 42℃, and each degree range is divided into 10 parts, so the thermometer can be accurate to 1/10 degree. The neck of the tube at the lower part of the thermometer near the bubble is a very narrow curved neck. When measuring body temperature, the mercury in the bubble expands due to heat, and the mercury can rise from the neck part to a certain position in the tube. When it reaches thermal equilibrium with the body temperature, the mercury column remains constant. When the thermometer leaves the human body, the outside temperature is low and the mercury shrinks in volume when it gets cold, so it breaks at the narrow curved neck part, preventing some of the mercury that has risen into the tube from returning, and the mercury column still maintains the height it reached when it came into contact with the human body.