One of the greatest animated serials of all time, "Superman", is now a comprehensive movie on YouTube. Every episode ever produced in the early 1940s, 1941 and 1942, have been combined into a YouTube movie that anyone on the Internet can watch for free.
Now you can see every episode and be an expert on the series. With incredibly impressive production quality for the time, that holds up every bit in our own day and age. Fleischer's Superman set a standard by which all other action adventure cartoons that followed hold homage to. You can clearly see the artistic influence of the series on shows that came much later, especially WB's Batman and the Superman TV cartoons that ran throughout the 1990s.
Here's the real thing in a comprehensive collection to enjoy. If you can't watch them all at this time, bookmark the YouTube link and you'll have it available at your pleasure. Here's the Forum Topic for your reference.