They are too old for Math Reviews, but I think the articles in question are:
Von Neumann: "Zur Prüferischen Theorie der idealen Zahlen", Acta Scientiarum Mathematicum (Szeged) 2:4 (1926) (can be read online at the journal's website)
Prüfer: "Neue Begründung der algebraischen Zahlentheorie", Math. Annalen 94 (1925), 198-243 (downloadable from the Göttingen archive)
in both of which one main idea seems to be (in modern language) to consider the embedding of a ring of integers $\frak{o}$ into the product $ \prod_{\frak{p},n}\frak{o}/\frak{p}^n$. The Von Neumann paper even mentions the $p$-adics. That's about all I could extract at a glance, my German being virtually nonexistent - someone with better German will be able do a more thorough job.