Several methods of determining moisture content of soil are in existence. The most accurate is the ovendrying method, in which an electric or portable gasoline oven is used to dry the samples. A more expedient method is the calcium carbide gas pressure method. This method, however, is less accurate and should always be approved by your supervisor. A third method uses the NUCLEAR MOISTURE-DENSITY METER. Since specialized training and operator certification are required, use of the nuclear moisture-density meter will not be discussed in this training manual.

As noted above, this is the most accurate method used to determine moisture content. The apparatus and procedures used are discussed below.

APPARATUS. Laboratory apparatus for moisture content determination includes the following items:

. A balance (fig. 15-26) for weighing material in grams. There are 453.6 g in a pound.

. Several small circular moisture boxes (called cans) (fig. 15-26) for placing samples in to weigh and dry.

. An electric oven or a portable gasoline oven to dry samples.

. Crucible tongs.

In the absence of an electric oven or gasoline oven, you may dry the materials in a frying pan held over an ordinary stove or hot plate. The

Figure 15-26.-Apparatus for determining moisture content.

disadvantage here is that the temperature is hard to control and the organic material in the sample may be burned; this would cause a slight to moderate inaccuracy in the result. The thermostat on an electric oven can be set to the desired temperature.