Elusive reels of tape full of nonsensical jamming, recorded by Deep Purple somewhere between June 2 and June 15, 1971 after an especially fruitless session in the recording of their Fireball album. The 1996 Anniversary Edition CD has an excerpt from these infamous tapes as track no. 13, featuring three songs: "Midnight in Moscow", "Robin Hood" (presumably some king of theme song to a TV show or a film) and "Wilhelm Tell" (the famous last part of the overture to Gioacchino Rossini's opera "Guglielmo Tell").
From the first notes on, it is already very clear that the band is very drunk, if not under the influence of various other substances. The stuff is screamingly funny, especially if you try to visualise the situation. All three songs are driven by Jon Lord hammering on an electric piano. "Wilhelm Tell" is the longest of the three pieces and has an interesting bass line -- the bass groove is that of "Highway Star", actually.
Some Data from the CD booklet. It also claims that two more pieces from that session, "Show me the Way to Go Home" and "Guitar Job" appeared on a 1980s solo record by Ritchie Blackmore.