What new attitude did Jim perceive in Silver? What discovery was made about the treasure?

Silver becomes determined and focused...... even bloodthirsty. Greed for the gold has taken over, and nothing else matters.

Silver hobbled, grunting, on his crutch; his nostrils stood out and quivered; he cursed like a madman when the flies settled on his hot and shiny countenance; he plucked furiously at the line that held me to him and from time to time turned his eyes upon me with a deadly look. Certainly he took no pains to hide his thoughts, and certainly I read them like print. In the immediate nearness of the gold, all else had been forgotten: his promise and the doctor's warning were both things of the past, and I could not doubt that he hoped to seize upon the treasure, find and board the HISPANIOLA under cover of night, cut every honest throat about that island, and sail away as he had at first intended, laden with crimes and riches.

At the end of the chapter, the pirates disciver the treasure has been dug up and moved.