Strain out the cabbage and you should be left with a bright purple liquid that you can use as a pH indicator. Place 3 tablespoons of each soil sample in a separate clear glass container. Pour 100 milliliters (mL) of hot cabbage juice indicator over each sample and let them sit undisturbed for 30 minutes. Compare the color of the cabbage juice indicator in each container. Soils with a nearly neutral pH will have little color change. If the solution is light blue, the soil is slightly alkaline, darker blues shading to green represent higher pH values. If the solution is a light pink the soil is slightly acidic, darker pink colors indicate lower pH values.