23 CONSTRUCTION MACHINERY AND EQUIPMENT-NAMELY, CONCRETE MIXERS, DERRICKS, HOISTS, HOISTING-ENGINES, STEAM-SHOVELS, CRANES, EXCAVATORS, AND BACK-FILLERS, STEAM PUMPS, GAS OR ELECTRIC POWERED CENTRIFUGAL PUMPS, GAS OR ELECTRIC POWERED DIAPHRAGM PUMPS, AND AIR OR ELECTRIC POWERED SUMP PUMPS, AIR COMPRESSORS, STEAM HAMMERS, STEAM AND GAS LOCOMOTIVES, AND ROAD ROLLERS