You mean HCl?
And it depends. If I had a hard drive that for some reason I didn't want anyone to get a hold of, I wouldn't put too much effort into destroying it, as data recovery methods are very expensive and I doubt that I'll ever have any data that would be worth thousands to someone to recover it.
I would probably just bang it with a hammer. Or take it apart, or just force the molex connector in upside down.
But if you really want 100% of the DATA removed HCl is the best bet. You have to break it down not only physically, but chemically. Also you could toast the discs with a blow torch.