All standard methods for determining carbon are so long and complicated as to setup and manipulation that a large number of determinations for total carbon in plant tissues are out of the question. The only colorimetric methods found were one for carbon in steel by the use of nitric acid, which has not proved very satisfactory, and one which measures carbon dioxide from wet combustion.2The latter takes considerable time and necessitates the handling of gases. A great need exists for a direct rapid method for determining carbon in carbohydrate and protein compounds commonly found in plants.When a carbohydrate or protein is heated with sulfuric acid, carbonization takes place, and the depth of color of the liquid is sensibly proportional to the amount of carbon present. Inasmuch as virtually all the carbon of plant tissue, especially vegetative tissue, is in the form of carbohydrate and proteins, and the proportion of carbon compounds that are not charred, such as oxalic acid or stable aromatic compounds, is very small, the color produced by charring with sulfuric acid should be a good index of the amount of carbon in the carbohydrates and proteins present. If it is known that nothing but carbohydrate or protein or substances which are completely charred are present it is an accurate method for determining total carbon.After complete carbonization the solution is diluted with 50 per cent H2SO4and compared to a standard in a colorimeter. The colloidal carbon solutions compare very well and give sharper end points than some colored true solutions.