First a word for @hivewatchers: if you do your research properly, as you should, you'll see that this post is published a day before the score is published on my website. Now, that would be quite a trick if I wasn't the original author, wouldn't it?
The 18th composition from manuscript Becker III.8.63 is a prelude in B flat major. It is a nice play with the motif introduced in bars two and three. The prelude wanders up and down the circle of fifths, thus giving it structure. The prelude starts in B flat major (obviously) and subsequently touches the tonalities of F major, d minor, g minor, c minor, f minor, E flat major, c minor, g minor and back to B flat major. The final bars are a long dominant section before the pece concludes on a B flat major chord.
The recording was done with the Sweelinq software and the sampleset of the Müller organ in the Grote Kerk, Leeuwarden (https://sweelinq.com/product/leeuwarden-nl-grote-kerk-muller-organ/).
The score will be available on my site tomorrow, with this link: https://partitura.org/index.php/josef-ferdinand-norbert-seger-praeludium-b-dur-l-18