Early Railroad Ties - Model Railroader Magazine

90% of the railroad track in the U.S. was laid with 21" tie spacing, and persists as such (if still wood tie) to this day.  Concrete ties are typically at 24" spacing.

Most of the main line and Class I railroads used ties circa 1900 that were 8' long, 6" x 8" dimensions.  High-tonnage railroads had started to go to 8'6" ties.  Hand-hewn ties were not uncommon even at that date on logging railroads and rural short lines in woods country like east Texas, Alabama, West Virginia. etc.

Until the 1930s most ties were untreated.

RWM