Assuming that a humus dried over sulfuric acid contains five per cent of hydrogen, the second calculation is made as follows. SECOND CALCULATION. 5.00 humus × 5 per cent = 0.25 per cent of hydrogen in humus corresponding to 2.28 per cent of water. Per cent. Water found 14.79 Difference = firmly combined water 12.51 THIRD CALCULATION. Per cent. Firmly combined water 12.47 Water from the hydrogen in humus 2.28 Total water 14.75 Found 14.79 In this way, in three other volcanic earths and in an ordinary alluvial clay from Rembang, there were found by analysis and by calculation the following percentages of water: 1. 2. 3. 4. 5. Percentage of water calculated 14.75 7.74 8.06 4.90 6.01 „ „ „ found 14.97 7.63 8.05 4.70 6.00 On the contrary, when the calculation is made from sea-slime taken from under the water a higher content of hydrogen must be assumed; _viz._, about six per cent. In two samples of sea-slime calculated in this way the following numbers were obtained: Percentage of water calculated 8.61 3.71 „ „ „ found 8.53 3.57 It is, therefore, quite evident that the organic compounds of soil taken from under the sea-water are richer in hydrogen than those exposed to the air or in cultivation. =303. General Conclusions.=—In the foregoing paragraphs have been collected the most widely practiced methods of determining moisture in soil in both a free and combined state. The following conclusions may serve to guide the analyst who endeavors to determine the water in any or all of its conditions: (1) In determining water in fresh samples the method of Whitney is satisfactory. Although the samples taken by this method are small they may be easily secured in great numbers over widely scattered areas, and can be easily transported without change. These samples should be dried at 100° to 110° for rapid work, or where time can be spared may be air-dried. (2) For a simple determination of the water left in the soil after air-drying (hygroscopic water) the method of the Association of Official Agricultural Chemists may be followed. There is much difference of opinion in respect of the proper temperature at which this moisture is to be determined. Much here depends on the nature of the soil. An almost purely mineral soil may safely be dried at 140° or 150°. A peaty soil, on the contrary, should not be exposed to a temperature above 100°. For general purposes the temperature chosen by the official chemists is to be recommended.