When adding, the dropper should be kept perpendicular to the top of the container, avoiding tilting, never upside down, and should not extend into the interior of the container or touch the container wall. Except for absorbing the solution, the tip of the tube should not come into contact with other objects to avoid contamination by impurities. It cannot be used in two ways. The ordinary dropper needs to be cleaned after use, while the specialized dropper cannot be cleaned. It needs to be used exclusively and can be replaced with the original reagent bottle after use.