The drying oven was a Blue M Model OV-490A-2 having two heaters each with a rating of 16.4 amps at 120 volts and employing forced-air circulation and temperature control within ± 1DC. Only two shelves located near the oven center were used to minimize errors due to temperature variations within the oven. The temperature of air in the vicinity of the sample containers was monitored using a precision mercury bulb thermometer. The sample containers had a diameter of 50 mm, a depth of 40 mm and were constructed of light gage sheet metal.