Clays and Clay Industries of Pennsylvania
Thomas Cramer Hopkins
Machine and hand, ..... 1888 40 90,000 || Air, ............ - - - - - 4 || 2 Martin. Hand, ..... ................ 1887 25 13,500 | Air, . ... 4 || 1 Martin. Hand and machine, ..... 1897 40 40,000 Air, ................. 4 || 1 Martin. Hand and machine, ..... 1888 16 9,000 || Air.