Um, duh, use a sharp edge on the scale to scrape away the surface on each ball until you find the pile with solid gold. Weigh one ball so that you only have 9 options left.

Or add balls sequentially until you find the 9 pounder, since that's only one weighing event, right??

Or scroll down for what I think the real answer is:





1 ball from first pile, 2 from second pile.... 9 from ninth pile, 0 from 10th pile, weigh it all up. If pile weight ends in 0, then gold is the unweighed (10th pile), if ends in 9 gold from 1st pile, if ends in 8 gold from 2nd pile... if ends in 1, gold from 9th pile. I win.