The lateral tube is then closed and the bottle is placed in a water-bath and kept at a constant temperature of 20°. When the temperature within and without the apparatus is the same the reading of the barometer is made, the stopper removed from the top of the cylinder, and the process of diffusion allowed to begin. After from six to ten hours the glass plate is moved so as to break the connection between the cylinder and bottle. The carbon dioxid remaining in the bottle is driven out by a stream of dry, pure air. The air is allowed to pass through the apparatus for about ten hours. The carbon dioxid driven out is collected in an absorption apparatus and weighed. The absorption apparatus should consist of a series of Geissler potash absorption bulbs and finally a =ᥩ= form soda-lime tube. In front of the absorption apparatus is placed a drying bulb containing sulfuric acid. Inasmuch as the temperature and pressure can be readily determined, the weight of carbon dioxid obtained is easily calculated to volume. The weight of 1,000 cubic centimeters of carbon dioxid at 0° and 760 millimeters pressure is 1.96503 grams. Therefore one milligram is equivalent to 0.5089 cubic centimeter of the gas. The volume of the bottle should be carefully determined by calibration with water. The results should be calculated to cubic centimeters per square centimeter of exposed surface in ten hours. The depth of the soil layer is conveniently taken at twenty centimeters. =288. Statement of Results.=— THE SOIL PACKED LOOSELY IN THE DIFFUSION TUBE. DIFFUSION TIME, TEN HOURS. Diameter of Weight of Pure carbon Carbon dioxid Cubic soil soil taken, dioxid at at end of centimeters particles, grams. beginning of experiment, of carbon millimeters. experiment, cubic cm. dioxid cubic cm. diffused for each square cm. 0.01–0.071 520 2549.4 1230.3 59.9 0.071–0.114 550 2545.9 1269.2 58.0 0.114–0.171 590 2556.4 1354.2 54.6 0.171–0.250 620 2538.9 1336.1 54.6 0.250–0.500 660 2532.0 1374.5 52.6 0.500–1.000 680 2528.2 1440.2 49.5 1.000–2.000 690 2496.6 1396.9 50.0 Mixture of 720 2514.3 1572.5 42.8 the above In greater detail the calculation and statement of the results may be illustrated by the following data: