PH test paper is usually used to test the acidity or alkalinity of a solution. Since it has a result color can have contrast, so roughly understand the degree of acidity and alkalinity of the solution, very intuitive and characteristic. First dip a clean glass rod into the liquid and drop it on the PH test paper. Then wait within 30 seconds to 1 minute. Compare the color of the test paper with the colorimetric card that comes with the test paper box, and the corresponding PH value that is similar to the colorimetric card is the PH value of the substance to be known. If the test paper has been contaminated or has exceeded its expiration date, it may affect the results of the test and cannot be used.