In the first experiment given in the above table the diameter of the soil particles varied from 0.010 to 0.071 millimeter. The weight of soil in the diffusion tube was 520 grams. The volume of gas, at 0° and 760 millimeters, before the diffusion began was 2549.4 cubic centimeters. The volume of carbon dioxid under standard conditions remaining after ten hours of diffusion was 1230.3 cubic centimeters. This volume is calculated from the weight of carbon dioxid obtained in the potash bulbs, each milligram being equal to 0.5089 cubic centimeter of carbon dioxid. The volume of carbon dioxid diffused is therefore 2549.4 − 1230.3 = 1319.1 cubic centimeters. The per cent of carbon dioxid diffused is 1319.1 ÷ 2549.4 = 51.74. The volume of carbon dioxid diffused for each square centimeter of cross section of the diffusion tube is 1319.1 ÷ 22 = 59.9 cubic centimeters. The carbon dioxid should be passed long enough to secure complete expulsion of the air before the determination is commenced. =289. General Conclusions.=—The general results of the experiments with the diffusion apparatus to determine the effect of the physical condition of the soil upon the rate of diffusion are as follows: 1. The diffusion of carbon dioxid through the soil is, at a constant temperature, chiefly dependent upon the pores in the cross section of the column of soil. Therefore, the absolute quantity of the diffused gas is greater the larger the total volume of the pores and _vice versa_. 2. Every diminution of the volume of the pores, whether secured by pressure of the soil or by an increase in the moisture thereof, is followed by a decrease in the volume of diffused gas. The giving up of the carbon dioxid present in the soil atmosphere to the upper atmosphere by the method of diffusion is therefore the less the finer the soil is, the more compressed the soil particles are, and the larger the water capacity of the sample and _vice versa_. 3. The quantity of diffused carbon dioxid is diminished according to the measure of compression to which the soil is subjected but is not strictly proportional to the height of the soil layer. 4. In soils in which rain water percolates slowly the diffusion of the carbon dioxid on account of this property is depressed to a greater or less extent. AUTHORITIES CITED IN PART FIFTH. Footnote 179: Proceedings of the American Association for the Advancement of Science, 1872, p. 328. Footnote 180: Die Landwirtschaftlichen Versuchs-Stationen, 1889, S. 197. Footnote 181: König, Untersuchung Landwirtschaftlich und Gewerblich Wichtiger Stoffe, Ss. 64–66. Footnote 182: König, op cit. supra. Footnote 183: Forschungen auf dem Gebiete der Agricultur-Physik, Band 15, S. 190. Footnote 184: Annales de Chimie et de Physique, Tome 37, 1853; Encyclopedie Chimique, Tome 4, p. 154. Footnote 185: Zeitschrift für Biologie, Band 7, S. 395 and Band 9, S. 250. Footnote 186: