Another method consists in thoroughly shaking about thirty grams of the soil in a graduated cylinder with fifty cubic centimeters of water containing a little ammonium chlorid and after twenty-four hours recording the volume occupied by the whole. The increase in volume over fifty cubic centimeters shows the quantity of water displaced. This method may also be used to determine the volume occupied by a soil when saturated with water. The above methods are only to be used when approximately correct results are all that are desired. =101. Apparent Specific Gravity.=—The apparent specific gravity of a soil is obtained by dividing its volume, interstitial spaces included, by the weight of an equal volume of water. The real and apparent specific gravities of six samples of soil are given below.[73] Real specific gravity 2.5445, 2.6315, 2.6508, 2.6400, 2.7325, 2.6603 Apparent specific gravity of air-dried soil 1.0940, 1.1710, 1.3570, 1.2810, 1.4060, 1.2730 Apparent specific gravity of soil dried at 125° 1.0990, 1.1770, 1.3750, 1.2910, 1.4640, 1.2850 It is to be noted that in computing the apparent specific gravity of a soil dried at 125° the volume occupied by the water is assumed to occupy the same space as if it existed in a free state. The volume of this water is therefore to be subtracted from the contents of the flask before proceeding with the computations. =102. Determination of Apparent Specific Gravity.=—Place in small quantity portions of the air-dried sample properly prepared, into an open glass cylinder, holding one liter, and about 170 millimeters high (if the height is exactly the mentioned one, the diameter of the cylinder will be 86.6 millimeters); pack the sample by striking the bottom of the cylinder hard against the palm of the hand after each new filling; close the cylinder thus filled by a glass plate and weigh on a balance sensitive to 0.1 gram; deduct the weight of the cylinder and glass plate, and the weight of one liter of soil in approximately similar conditions as it is found on the dry land prepared for cultivation, is thus ascertained. The weight of one liter of the soil in grams multiplied by 2000 will give in kilograms the weight of the surface soil from a hectare (2.47 acres) of the field from which the sample is taken when the depth of this is calculated at twenty centimeters.[74] RELATION OF THE SOIL TO HEAT.