MACHINES positive displacement rotary or oscillating piston liquid and elastic fluid or elastic fluid liquid only reciprocating piston or other liquid and elastic fluid or elastic fluid liquid only non-positive displacement liquid and elastic fluid or elastic fluid liquid only ENGINES positive displacement rotary or oscillating piston liquid and elastic fluid or elastic fluid liquid only reciprocating piston or other liquid and elastic fluid or elastic fluid liquid only non-positive displacement liquid and elastic fluid or elastic fluid liquid only PUMPS positive displacement rotary or oscillating piston reciprocating piston or other non-positive displacement This class covers: furnaces, kilns, ovens, retorts, open sintering apparatus and other similar apparatus for heat treatment of materials or articles, and details or accessories therefor, in general; the arrangement of electrical heating elements in or on furnaces. This class does not cover: combustion apparatus per se, i.e. apparatus for direct combination of oxygen gas and a burnable substance; electrical heating elements per se; processes carried on within the furnaces. In this class, the following term is used with the meaning indicated: "furnaces" covers kilns, ovens, or retorts. Attention is drawn to the references and Notes following the title of class and the Note(3)of section H. FURNACES WITH STATIONARY CHARGE Shaft furnaces Horizontal furnaces , Bell-type furnaces With progression of heating Crucible furnaces, tank furnaces STATIONARY FURNACES WITH MECHANICALLY-MOVED CHARGE ROTARY FURNACES , OTHER FURNACES; COMBINATIONS , ; OPEN SINTERING OR LIKE APPARATUS Attention is drawn to the references and Notes following the title of class and Note(3) of section H. CONSTRUCTIONAL FEATURES HANDLING AND SUPPORTING CHARGE , , PREHEATING CHARGE; COOLING; USING WASTE HEAT OR GASES ; , ; ARRANGEMENTS OF ELECTRIC HEATING ELEMENTS ARRANGEMENTS OF CONTROL AND SAFETY DEVICES , OTHER FEATURES; OTHER DETAILS ;