"Under a cooperative agreement dated April 4, 1951, the American Air Filter Company, Inc. supplied a size 3/4, type-N Rota-Clone for tests in recovering shale-oil particles from a gas stream. The tests were conducted by the U. S. Department of Interior, Bureau of Mines, at its Oil Shale Demonstration Branch, Rifle, Colorado. The testing of the type-N Roto-Clone is part of an investigation to discover the most feasible method for recovering 98 to 100 percent of the shale-oil mist and/or spray particles which are produced from various oil-shale retorting processes."