_Method C._—The same flat dish and the same quantity of soil as in the other methods are taken in this one. The sample is left out over night where it can be fully saturated with dew. The amount of dew which appears on the bushes should be noted and also the temperature of the air and the percentage of clouds in the sky. An experiment should also be made on spots of earth which are entirely free from vegetation in order that the difference in the amount of water absorbed in places practically devoid of dew and in places where the dew is abundant may be observed. _Method D._—Deeper flat dishes should be used for this determination so that the depth of soil contained in them shall be from one to three, or even six centimeters. The sample of soil should be completely air-dried and in a state of fine subdivision. The vessels containing the soil should be placed in a locality saturated with aqueous vapor or in the open air during the night where they are subjected to the influence of the cooling of the atmosphere and the deposition of dew. Note should be made of the different amounts of moisture absorbed by the layers of earth of different thicknesses in a given time. Observation should also be made of the depth to which the moisture sinks in the sample of soil under consideration. =282. Estimation of the Absorption Power of the Soil for Oxygen and Atmospheric Air.=[182]—From fifty to one hundred grams of air-dried soil are placed in a glass vessel of about 500 cubic centimeters capacity, and the flask closed with a stopper after the addition of enough water to make the percentage of moisture in the soil about twenty. After from eight to fourteen days the air contained in the vessel is analyzed for oxygen, nitrogen, and carbon dioxid, with special reference to the determination of how much oxygen has disappeared and how much the carbon dioxid has been increased. As an alternative method, twenty-five grams of the soil may be moistened with tolerably concentrated potash lye in a small glass vessel, which is itself joined with air-tight connections to an azotometer in which a known volume of air is confined by quicksilver. The glass vessel is frequently shaken during the progress of the experiment. The diminution of the volume of air in the apparatus after from one to four days gives approximately the quantity of oxygen absorbed. =283. General Method of Determining Absorption.=—This method, due to Freiherrn von Dobeneck,[183] is as follows: The soil, in a state of fine powder, is dried at 100° to 105° to a constant weight. It is then placed in an absorption tube of the following construction: