Invented in antiquity, early processes of metalwork such as smelting and rudimentary welding were made possible by the bellows. Such endeavors required intense heat, and bellows provided additional air to enhance the modest heat of the forge. Bellows also powered musical instruments, such as reed or pipe organs. Compression of air using bellows produced heat, and its expansive rarefaction produced cold. Experience with bellows in common fireplaces led to refined and improved alchemical forges. Problems with the soft iron rails of early railroads and the boilers and cylinders of steam engines encouraged experimentation with higher smelting temperatures and refined metallurgy. Andrew Carnegie brought the so-called Bessemer process to the United States, where injection of superheated air and trace metals at just the right time resulted in high-strength steel. Similarly, continuously operating bellows were applied to musical instruments to produce the grand and sublime experiences of massive church organs.