Granted Patent
Utility
US 4,017,121 · App. 05/572,250
Longwall mining of trona with prefracturing to prevent slabbing
Inventor:
Robert H. Trent
Patented Case
View Patent ↗
Granted: Apr 12, 1977
Filed: Apr 28, 1975
Inventor
Robert H. Trent
Assignee (at issue)
Allied Chemical Corporation
This patent predates the USPTO's electronic file wrapper — prosecution documents from this era exist only in the Patent Office's paper records. A certified copy of the file history can be ordered from the USPTO's paper archives.