Newlands' law of octaves worked well only with the-

 Newlands' law of octaves is applicable only to the lighter elements. The pattern will change when the weight is increased.
He arranged them in an ascending order based on their atomic masses and observed that every 8th element had similar properties. 

Hence, Newlands' law of octaves worked well only with Lighter elements that mean which are present at the start of the periodic table.