Merging disk partitions

I recently created a 2nd partition of 50GB to test Yosemite and have now installed in my main partition (Macintosh HD) after deeming it was stable enough. I now have the 50GB partition which I wish to merge back into he primary partition as I have no need for it. In Disk Utility it currently looks like this:

When I go to delete the second partition it won't allow me as it is formatted as Free Space. I try to reformat the same as the primary partition (Mac OS Extended) but it doesn't actually do anything.

So now I have this secondary partition that I can't seem to do anything with. I've tried using Disk Utility both within the OS and also by booting into the Disk Utility via a boot disk, but both result in the same problems. The only thing that may be contributing is that FileVault is enabled on the primary partition. Could this be stopping them from merging?

Any ideas on how to delete the secondary partition and merge it back into the first?