The melting point is the equilibrium temperature between the solid state and the liquid state of a substance under atmospheric pressure. It is usually measured as the temperature of a crystalline substance changing from a solid state to a liquid state, and it is recorded as the melting point. Melting point is an important method for identifying substances and determining the purity of substances. Therefore, melting point testers have an important position in the chemical industry and medical research. It is an essential instrument for the production of drugs, fragrances, dyes and other organic crystal substances, and is also commonly used in laboratories as one of the basic instruments.

Pure solid substances generally have a fixed melting point and a short melting range, generally not exceeding 0.5-1 ℃. Through this point, the purity of the substance can be determined and the unknown substance can be identified. The unknown substance is mixed with the known substance to determine the melting point. If the melting point does not change and the melting range does not exceed 1°C, it can generally be considered that the two are the same substance. This method is called the mixed melting point method.

At present, the main method for testing the melting point is to use a melting point tester. The manufacturing standard of the melting point tester is the nationally regulated JJG 701-2008 verification procedure. Because of its simple operation and clear results, especially the automatic melting point tester that does not require laboratory personnel to monitor at any time, melting point tester is very popular among users.

There are many types of melting point testers on the market, and there are various brands. How to choose a suitable melting point tester can refer to the following aspects:

I. The test conditions of samples
For powdered samples, a melting point tester based on capillary melting point determination can be used. According to specific indicators like whether the sample is transparent after melting, the initial melting of the sample, the melting range, we decide to choose a visual melting point tester based on silicone oil method or a fully automatic melting point tester. For flake or block samples, a microscopic melting point tester can be used.

II. Test accuracy, results repeatability and range
The accuracy of the test, the repeatability of the test results and the test range are all references for choosing a melting point tester. According to actual needs, after meeting the measurement range, the higher the accuracy and repeatability, the better it is.

The melting point tester needs to be calibrated when it is turned on for first time or has been used for 1 year. Long-term use and seasonal temperature differences will cause large errors in the instrument. Basically, it must be calibrated every 1 year. According to different needs, it will be sent to the relevant technical supervision bureau for verification, and the department will issue a report based on the verification result. If the results do not need to be reported by the relevant authority, the instrument can also be sent back to the purchasing company for calibration, or we can buy standard products to calibrate it by ourselves according to the calibration procedure.