observe sample color by filling a matched nessler tube to the 50 ml mark with sample and comparing it with standard. look vertically downward through tubes toward a white or specular surface placed at such an angle the light is reflected upward through the columns of liquid. if turbidity is present and has not been removed, report as apparent color.if the color exceed 100 units dilute sample in known proportions until the color is within the range of the standard.