It's actually on the page (far right middle) and it expired in 2015, which is 20 years after filing (plus any extensions due to delays). Actually, applications

It's actually on the page (far right middle) and it expired in 2015, which is 20 years after filing (plus any extensions due to delays). Actually, applications before 1996 can be a bit trickier since they (and their children) can be extended for quite a while (that's what some IP firms did in the early 2000s) by delaying their issuance. Patents were originally good for 17 years after issuance (or 20 years from filing if that was longer), whereas now it is only 20 years from filing.