Students can test solutions for acid or base determination. Easy-to-use red litmus paper turns blue for bases and blue litmus turns red for acids. 100 strips of each. Not for measuring the pH of natural waters, such as streams, rivers and lakes. </br></br>Instructions:</br> Remove one litmus test paper from the vial, being careful not to touch the strip anywhere other than where you grasp it.</br> Dip the strip into the solution to be tested for 1-2 seconds and remove.<br> The red test strip will turn blue in seconds if dipped into a solution that is a base, and will remain unchanged if not. The blue test strip will turn red in seconds if dipped into a solution that is a base, and will remain unchanged if not.