My question is this: what pieces of iron? This book is the only place I've seen it mentioned, and every time I read the book it makes me curious. Is anyone familiar with the practice of having pieces of iron sitting in the bottom of an iron kettle? Do these things have a name? Can they be purchased?The kettle sings well, for pieces of iron are so arranged in the bottom as to produce a peculiar melody in which one may hear the echoes of a cataract muffled by the clouds, of a distant sea breaking among the rocks, a rainstorm sweeping through a bamboo forest, or of the soughing of pines on some faraway hill.