Table 3. Patent classes searched. 



Class code Class title 



9 Boats, Buoys, and Aquatic Devices 



14 Bridges 



35 Education 



37 Excavating 



43 Fishing, Trapping, and Vermin Destroying 



52 Static Structures, e.g.. Buildings 



60 Power Plants 



61 Hydraulic and Earth Engineering 

 73 Measuring and Testing 



94 Roads and Pavements 



102 Ammunition and Explosive Devices 



114 Ships 



115 Marine Propulsion 



117 Coating: Processes and Miscellaneous Products 



137 Fluid Handling 



141 Fluent Material Handling, with Receiver or 



Receiver Coacting Means 



166 Wells 



172 Earth Working 



173 Tool Driving or Impacting 



174 Electricity, Conductors, and Insulators 



175 Boring or Penetrating the Earth 



181 Acoustics 



182 Fire Escapes, Ladders, Scaffolds 



185 Motors, Spring, Weight, and Animal Powered 



204 Chemistry, Electrical and Wave Energy 



210 Liquid Purification or Separation 



214 Material or Article Handling 



239 Fluid Sprinkling, Spraying, and Diffusing 



249 Static Molds 



250 Radiant Energy 



252 Compositions 



253 Motors, Fluid 



264 Plastic and Non-Metallic Article Shaping 



290 Prime-Mover Dynamo Plants 



299 Mining or In Situ Disintegration of Hard 



Material 



302 Conveyors, Fluid Current 



324 Electricity, Measuring, and Testing 



340 Communications, Electrical 



356 Optics, Measuring, and Testing 



415 Rotary Kinetic Fluid Motors or Pumps 



417 Pumps 



15 



