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ES140493A1
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An improved system apparatus for sound conduction.
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Improvements in and relating to Rock Drills and the like.
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Improvements in and relating to Apparatus for the Extraction of Metals from their Ores.
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Improvements in Machines for Pulverizing, Crushing and Grinding
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CA296133A
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Telephone accessory
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CA368460A
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Sound conducting apparatus
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Sound conducting apparatus
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Telephone headgear attachment
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Telephone instrument
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Telephone accessory
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