Red Thermometer vs Mercury Thermometer

The principle of thermometer measurement

Zeroth law of
thermodynamics

The zero law of thermodynamics is the basic basis for system measurement:
①By making two systems come into contact, and observing whether the properties of the two systems have changed, it is judged whether the two systems have reached equilibrium;
②When the external conditions do not change When the system has reached a thermal equilibrium state, the internal temperature is evenly distributed, and has a fixed temperature value;
③all systems that are in equilibrium with each other have the same temperature, so the temperature of one system can be balanced by another It can be expressed by the temperature of the system; or it can be expressed by the temperature of the third system.

Temperature scale

The temperature scale is the abbreviation of the standard quantity of temperature. The determination of the temperature scale includes the selection of measuring materials, the selection of fixed points, the division of temperature values, etc.; the common temperature scales include the thermodynamic temperature scale (Kelvin 1848), the international practical thermometer (the second-level standard of the temperature scale) ) And other temperature scales.

Classification of thermometers

Commonly used thermometers include mercury thermometers, alcohol thermometers （spirit thermometer） , and kerosene thermometers. They are all manufactured according to the principle that the liquid filled with the thermometer expands when heated and contracts when cold. The temperature measurement range of the thermometer is determined by the boiling point and freezing point of the filled liquid, and the softening temperature of the glass used. The upper limit of the temperature measurement of the thermometer made of general glass does not exceed 360°C, and the thermometer made of special glass can reach 1200°C.

What is mercury thermometer：

The freezing point of mercury thermometer is -38.87℃. The boiling point of mercury is 356.7℃ under one atmosphere. In order to prevent mercury from being oxidized and increase the boiling point of mercury, thereby increasing the upper limit of temperature measurement of mercury, the air in the thermometer is evacuated and charged during manufacture. Use inert gas, such as helium, argon or nitrogen. If the pressure of nitrogen gas is 2.5×10^6Pa, the upper limit temperature of measurement is 550℃. If the pressure of ammonia gas is 7×10^6Pa, the upper limit temperature of measurement is 750℃: the measuring range of mercury thermometer can reach -30℃~+ 1200°C

What is alcohol thermometer （spirit thermometer）：

The freezing point of alcohol is -112°C and the boiling point under normal pressure is 78.4°C. The instrument factory manufactures alcohol thermometers and tries to increase the boiling point of alcohol by pressurizing the temperature measuring liquid column by about 3×10^5Pa. The measuring range of the alcohol thermometer is -100℃~+200℃

What is kerosene thermometer：

Kerosene is an organic compound. In petroleum products, molecules with C11~C16 carbon atoms are collectively referred to as kerosene. Therefore, kerosene has a variety of different grades. Its boiling point and freezing point are 110~325°C and freezing point -10°C under normal pressure. According to some manufacturers’ data, the temperature measurement range of kerosene thermometers is -50~+200°C. The liquid column of the kerosene thermometer is not aerated and pressurized.

The alcohol（spirit） and kerosene in the thermometer are usually dyed red，So the alcohol thermometer and kerosene thermometer are collectively called red thermometer.

Red mercury thermometer does not exist

The reason for the name ：red mercury thermometer

1.Since many people’s first image of a thermometer is a mercury thermometer, some people named it red mercury thermometer directly after seeing the red thermometer.

2.When naming products, many merchants took the name red mercury thermometer for the convenience of naming multiple products at once.

3.Many merchants use multiple words at the same time in order to increase the search volume of products.

4. Because the name red mercury thermometer is commonly used in many large trading platforms, people think that the name is correct.

why red mercury thermometer does not exist

Because of the appearance of the name red mercury thermometer, many people think that the liquid in the glass is red mercury, but in fact, red mercury only existed in movies，And scientists have yet to prove that red mercury is real.

And mercury cannot be dyed ，So naturally occurring mercury cannot be red, so naturally there will be no red mercury thermometer.

So in fact, all the thermometers named red mercury thermometers you see or on the market are alcohol thermometer（spirit thermometer） or kerosene thermometer,Inside the glass is alcohol（spirit） or kerosene.

mercury thermometer will also disappear

Standard mercury thermometer is one of the commonly used standard instruments in temperature measurement, and it is widely used in many industries. Announcement No. 38 issued by the former Ministry of Environmental Protection in conjunction with relevant ministries and commissions in 2017: The Minamata Convention on Mercury has entered into force for China on August 16, 2017, which clearly prohibits the production of thermometers and thermometers containing recordings from January 1, 2026. Sphygmomanometer containing mercury. On October 16, 2020, the State Food and Drug Administration issued the “Notice of the Comprehensive Department of the State Food and Drug Administration on Matters Concerning the Implementation of the Minamata Convention on Mercury”, expressly requiring that from January 1, 2026, China will completely ban Production of mercury-containing thermometers and mercury-containing sphygmomanometer products. Therefore, the replacement of standard mercury thermometers is very urgent and needed. Products that replace standard mercury thermometers should meet the requirements in terms of technical indicators and measurement standard stability, so as to meet the demand for value transmission and traceability. At the same time, they should have a certain degree of universality and technological advancement.

Standard mercury thermometers are standard measurement instruments in the national temperature measurement instrument verification system, and can be used as measurement standards for most working measurement instruments, such as industrial platinum resistance thermometers, digital thermometers, mercury thermometers, etc. The harm of mercury to the environment and human health has attracted increasing attention. Because of this, the “Minamata Convention on Mercury” has been recognized and paid attention to by many countries in the world.
China is the world’s largest producer, consumer and emitter. A mercury thermometer contains 1g of mercury. After all of it evaporates, the mercury concentration in a 15m² room can reach 22.2 mg/m³, and ordinary people in a room with a mercury concentration of 13mg/m³ , 2h may cause headache, fever, abdominal cramps, dyspnea and other symptoms. The standard mercury thermometer contains about 8~10g of mercury, and the potential harm caused by it is even more serious.

The research on the substitution of standard mercury thermometers can realize the smooth transition of our country’s temperature measurement system, which is of great significance for smoothly advancing the implementation of the “Minamata Convention”.

Therefore, alcohol（spirit） thermometer and kerosene thermometer will gradually become the mainstream of industrial thermometer