I like to study monetary history -- yup, read Friedman & Schwartz' magnus opus in college -- and doing some readings the last year or so with books spanning the gold standard to 1921 Recession and The Great Depression. The changes in the writings concerning gold, silver, and legal tender are fascinating. Even as a young collector (or spender of bills ! ) I never really paid too much attention to them but you can see there are big differences and the changes over the years WERE important. Here's a Gold Certificate, and the seal writings clearly state you are entitled to Gold...and the writing at the bottom of the obverse says gold coin (Eagles, DEs, etc.) Notice that it is good for ALL DEBTS with no exceptions. Next we have a United States Note (Red Seal) which states it is legal tender....for all debts public and private.....but then says "except duties on imports and interest on the national debt." Why these obscure exclusions ? Because the Treasury didn't want a gold drain out of the U.S. so NOT allowing these to be used for duties on imports and interest on the national debt helped towards that goal. Next up, a 1928 Federal Reserve Note which says that is was redeemable in gold...on demand....at the U.S. Treasury (so you had to goto Washington, DC I guess). What I find interesting is that at 1st glance this bill looks like a hybrid: it's a FRN...it's worth $20 dollars ("bearer on demand" language at bottom)...but it has the quasi-gold certificate language above the seal. But while you could get gold at the Treasury, it's unclear if the FRB's that you went to could pay you off with gold or a pair of $10 bills at their choice... or your choice. Again, unless Federal Reserve Bank means a MEMBER bank, then FRB means you would need to goto 1 of the 12 actual physical locations which would be a PITA. Lastly, after we went off the Gold Standard we have this FRN which says that the note is legal tender for ALL debts public and private with no exceptions regarding national debt or imports. I guess "redeemable in lawful money" (isn't this bill lawful money ? ) means a pair of $20's and a $10 bill. Also known as....change !!
Feel free to add others I missed from the Small and especially Large Bill eras. I don't have any large bills myself, but I'm sure the verbiage changed from 1863 to the 1920's.
United States Notes: Besides the Red Seal, the notes didn't have a $10, $20, or $50 denomination. They were issued from 1862 to 1971. I still don't know why we had USN's and FRN's being issued at the same time -- you'd think there'd only be 1 type of currency bill (aside from the years with GC's and SC's). The bulk of federal revenues came from import duties (no federal income tax until 1913 ! ) so the government wanted gold and not paper for those fees. On interest on the national debt: the fear was that being able to pay in paper would collapse the bond prices so paying interest in gold was seen as maintaining the creditworthiness of the United States (smart move !). That's why you had these 2 weird exclusions specifically listed. In the 1930s, this USN legalese would be changed to: "This note is a legal tender at its face value for all debts public and private."
