The most reliable method of obtaining representative samples from heterogeneous granular and powdered materials is through a rotary sample splitter (also known as a spinning riffle). A study by A. A. Kahn, Ph.D., Bradford University 1968, which was also published in the May 1970 CHEMICAL ENGINEERING magazine, concluded that rotary sample splitters are the most accurate method of extracting representative samples from dry, granular, or powdered material. This type of unit minimizes the negative influences of diverse and extreme differences in grain size, specific gravity, average quality, and particle shape.