Filters, namely, air filters for domestic use, air filters for industrial installations, water filters; gas scrubbing apparatus; boilers, other than parts of machines, namely, electrical boilers, heating boilers, furnace boilers, industrial boilers; water purification installations; air purifying apparatus and machines; purification installations for sewage; water purifying apparatus and machines; oil-scrubbing apparatus, namely, industrial scrubbers for removing particulate matter from the air during industrial processing in the nature of impingement scrubbers, venturi scrubbers, dynamic scrubbers; sewage treatment equipment, namely, waste water treatment tanks, clarification and thickening machines for use in treatment of liquids in the nature of water, waste water and industrial water, chemical sterilization units, particle activators for use in drinking water treatment and in municipal and industrial wastewater treatment