Yes it appears to be medium format slide film. You
can get slide film in 35mm format you know. Anyway, the format is irrelevant to the point I was trying to make - I was just showing an example of what one might expect from expired film, so hopefully you would see that you could use it for experimentation rather than throwing it in the bin.
As for negative, check the flickr link that riot sky posted (
http://www.flickr.com/groups/expired/pool/) - there are plenty of examples of out-of-date 35mm negative film on there.
Hey, if you don't want to use it then send it this way, I'd be more than willing to experiment with it.