These burettes prevent contamination of media by outside elements. Feature easy-to-read blue graduations against white background. Flexible vinyl fill tube connects burette top with vinyl bottle stopper and extends into bottle. Operate the unique push-button stopcock using thumb pressure for drop-by-drop delivery. Small screw clamp lets you preset drop speed for repeat titration. LDPE bottle and tube, vinyl stopper, glass burette, PP stopcock. Bel-Art.