Jahresbericht für Agriculturchemie, Band 1, S. 160. Footnote 187: Annales de Chimie et de Physique, 1891, Sixième Série, Tome 23, pp. 362, et seq. Footnote 188: Op. cit. 5, 1892, Ss. 8, et seq. PART SIXTH. =290. Preliminary Considerations.=—The sample of soil intended for chemical analysis should consist of the fine earth which has passed at least a one-millimeter mesh sieve and subsequently been completely air-dried. According to Petermann the air-drying of a soil should continue for about four days for an ordinary arable soil, and about six days for one very rich in organic matter. With peat and muck soils I have found that ten or twelve days with frequent stirring, even when in thin layers, are necessary to attain approximately a constant weight. The soil is conveniently spread on a zinc or other metal sheet of sufficient area so that the layer will be only one or two centimeters in thickness. The weight before and after desiccation will give the percentage of moisture lost on air-drying, which, of course, will depend chiefly on the degree of saturation of the sample when taken and the atmospheric conditions prevailing during drying. If samples of soil are taken in very dry times it is often necessary to moisten them with distilled water in order to prepare them properly for air-drying. The quantity of hygroscopic water which the sample loses at 100°–105° should be determined, and all subsequent calculations of the percentages of the various constituents be based on the water-free material. When a soil which has been dried at 100°–105° to a constant weight is heated to 140°–150° it loses additional weight not due to loss of water of constitution. A part of this loss may be due to hygroscopic moisture which is not given off at 100°–105°, and a part may be hydrocarbons, or other easily volatile organic or inorganic bodies. Before estimating the total loss on ignition it is recommended by most chemists to dry at 140°–150°. The samples of soil, however, intended for chemical examination should never be dried beyond the point which is reached by exposure in thin layers at ordinary room temperatures. The state of aggregation, degree of solubility, and general properties of a soil, may be so changed by absolute desiccation as to render the subsequent results of chemical investigation misleading. In the methods which follow the actual processes employed have been given, which in some instances transgress the general principle stated above, but in all cases standard and approved methods are given in detail, even if some of their provisions seem unnecessary or imperfect.