A better defined result is obtained in carefully burning a known weight of earth either in a current of free oxygen, or with lead chromate. The water produced in such a combustion is secured in a =ᥩ= tube filled with pumice stone saturated with sulfuric acid, the carbon dioxid being absorbed afterwards in potash bulbs and by solid potash. The weight of earth burned is chosen so as to furnish a convenient weight of both water and carbon dioxid. In general about five grams are sufficient. When the combustion is made with oxygen, the soil is contained in a boat and the products of the combustion are carried over a long column of copper oxid heated to redness. The residue left in the boat is weighed at the end of the operation, and in this residue it is advisable to determine any undecomposed carbonate. Should the sample burn badly and be mixed with carbonaceous matter at the end of the operation, it will be necessary to substitute the lead chromate method. In this case, of course, the residue left after combustion is not weighed. Whichever method is employed gives a quantity of water originally combined with the soil, plus the quantity arising from the combustion of the hydrogen of the organic matter. The details of the processes for organic combustion, will be given in a subsequent part of this manual. It is not possible to divide the water between these two sources directly, but this can be done by calculation, which gives results lying within the limits of probability. The method follows: The organic nitrogen, determined separately, by soda-lime, the method of Kjeldahl, or volumetrically, is derived from proteid principles resembling albuminoids containing about one-sixteenth of their weight of nitrogen. The nitrates contained in the earth are in such feeble proportion, as to be negligible in this calculation. The total weight of these nitrogenous principles in the soil is therefore easily calculated. The carbon contained in the proteids is then calculated on a basis of 53 per cent of their total weight, and the hydrogen on a basis of 7.2 per cent. From the weight of the total organic carbon (determined as described further on) is subtracted the carbon present in the proteids. The remainder corresponds to the organic carbon present as carbohydrates, (ligneous principles) containing 44.4 per cent carbon and 6.2 per cent hydrogen. By adding together the weight of the hydrogen contained in the ligneous principles, and the hydrogen contained in the proteids, and multiplying the sum by 9, the weight of water formed by the combustion of all the organic matter in the sample is obtained. This is subtracted from the weight of the total water obtained by direct determination as described above. The difference represents the weight of water combined with the silicates, etc., as well as with organic matters.