Follow this link to go to the official Runescape forum thread for Solum. There are instructions there for how to apply.
http://services.runescape.com/m=forum/a=13/sl=0/forums.ws?320,321,279,65515837
QFC for the thread: 320-321-279-65515837
http://services.runescape.com/m=forum/a=13/sl=0/forums.ws?320,321,279,65515837
QFC for the thread: 320-321-279-65515837