Normal silica gel desiccant is no color, is the true color of silica gel, after the tide will not change color. Silica gel to change the color is added to the cobalt chloride. The color is changed from blue to pink. The silica gel in cobalt chloride solution soak, take out dry, in the oven, to 105 degrees Celsius drying, this time cobalt chloride dehydration into blue, you can use the. When the silica gel water absorption gradually increased, cobalt chloride water, and gradually become pink, which is a gradual process, pink to a certain extent, indicating that the silica gel has lost the ability to absorb water.