I have some sewage pipes in my basement that I have to remove because one of them is cracking and leaking. The problem is that I can't get the joints apart. Does anyone know how to remove the sealing compound for old cast iron pipes. They were put in around 1945 so I am pretty sure that there is lead in the joint

You are correct. The joints are lead and oakum. When I have a piece of faulty cast iron I take a 22 ounce hammer and break the bell end of the pipe, take it out in pieces and then cut the lead ring with a sharp chisel and pull it off. The spigot end takes a different approach. About a foot away from the joint start to bust up the cast iron. Work your way up to the joint. By this time you should have cracked the pipe to the end where you can start pulling it out of the bell in pieces. Once you get the first few pieces out the rest is easy. You are left with the lead ring in the bell. As a rule I just take a screwdriver, pry it up and then pry it out but you can take a sharp chisel and cut it in two and then pry it our. You now have it out, what's your game plan for replacing it?
Cheers, Tom

I'm not an expert like speedball so perhaps this is not the best way but...

If I have enough room I cut out the bad portions of cast iron pipe with a reciprocating saw. Then I use fernco (or similar) couplings to relace the cut out section with PVC.

http://www.fernco.com/coupling.html

Should be easy enough. Good luck.

OK, so to be a little more specific with my issue since that sounds like the way I will have to go. I have cast iron that runst to the drain line for my upstairs sinks, this line is steel, and I can't remove this line. But I need to replace the cast iron. So, if I read the post right then I should be able to crack the cast iron at the bell and then chisel the lead and okum away right?

ok, so to be a little more specific with my issue since that sounds like the way i will have to go. i have cast iron that runst to the drain line for my upstairs sinks, this line is steel, and i can't remove this line. but i need to replace the cast iron. so, if i read the post right then i should be able to crack the cast iron at the bell and then chisel the lead and okum away right?

Right! Cast iron is a brittle metal that will break easily. But cast iron is also very hard so if you plan on cutting it in two with a reciprocating saw you better have a bunch of extra metal blades and a lot of time and patience.
The only way to cut cast iron is with a set of cast iron snap cutters or, (if in a tight spot) ,a set of ratchet chain cutters. Could you be a little more specific about with what and how you intend to replace the cut out cast iron. Regards, Tom

I am going to use pvc to replace the cast iron. I am trying not to have to cut it because there is no room around it to move. I am going to try to break it the way that you suggested.

Sounds good and good luck. Speedball is right about having a few blades around if you go with a recip saw...

Once I cut through some 4 inch clay pipe with a recip. Saw with tungsten carbide blades... made a nice cut but took forever and used about 8 blades for 2 cuts... guess I just love that saw!