This two-tube inclined retort, known as a "Rossi Retort," was named for Louis Rossi who came to New Almaden in the 1920s and built a reduction plant based on his patented design. This style of retort allowed rapid recovery of valuable mercury from high-grade ore.
In operation, the retort was charged with up to 400 pounds of crushed ore per cylinder, sealed, then heated for 8 to 24 house. The mercury sulfide vapors traveled up through the two condenser pipes, where the vapor cooled back to liquid mercury. The condenser pipes terminated into rubber buckets filled with water. Sulphur gases, a byproduct of the roasting process, were released through the chimney on top of the bucket cabinet.
Ore for the retort sat in the dump-truck bed above the retort. A knife gate mechanism regulated the ore feed and would only permit pieces less than 3 inches in size. Fresh ore was fed into the tubes by way of the triangular apron at the bottom of the truck bed.
The Rossi retort was unique because it used a perfect "angle of repose" to ensure the ore chambers were never completely full, thereby allowing freedom of gas movement and ready collection of the escaping mercury vapor.