This section is from the book "The Potato: A Compilation of Information from Every Available Source", by Eugene H. Grubb, W. S. Guilford. Also available from Amazon: The Potato: A Compilation Of Information From Every Available Source.
The Thompson potato sorter is made by James Thompson, Greeley, Col., and is largely used in the West. Mr. Thompson also makes bag holders and potato baskets. The sorter is operated by rocking back and forth the part into which the potatoes are emptied, the small potatoes dropping through the screen and being conveyed into one sack, the larger ones going over the screen and into the other sack. It is used both in the cellar and field.
By laying a burlap sack over the upper end of the screen there is less bruising of the potatoes as they are shoveled or emptied on the sorter. The sack may cover one quarter to one third of the top surface of the sorter.
Thompson's Greeley Potato Sorter.