An Aluminum Block Digester for Plant and Soil Analysis

Abstract Almost every institution, whether it be a university, a government agency, or a medical or industrial facility, that conducts research on and is concerned with the elemental analysis of biological material has a need for equipment to ash or acid‐digest samples. Often funds are not available with which to purchase commercial equipment and the researcher is required to be innovative and to design and engineer his own. Because of the lack of research funds and a need for soil and plant analysis equipment, this study was made to design and construct a large capacity, electrically‐heated and thermostatically‐controlled aluminum block digester for plant and soil samples. A drawing was prepared giving dimensions needed for shop‐work to be performed. A block of aluminum 10.2 cm (4 inches) thick was used. The block has a capacity of 126, 2.54‐cm (1 inch) diameter test tubes. The overall block dimensions are 10.2 cm (4 inches) thick, 35.6 cm (14 inches) wide, and 55.1 cm (21 11/16 inches) long. Electric heater strips are bolted to the block inside 1.9‐cm (¾ inch) milled slots. The temperature control sensor is a thermocouple inserted into the block and wired to the thermostat controller. The block heats almost linearly from room temperature to 240C at a rate of almost 4C/minute. The heating rate from room temperature to 375C is over 2C/minute and requires 2.5 hours heating time.