It is an interesting fact that while the racing on the Mississippi resulted in the explosion of many boilers and the consequent loss of hundreds of lives, no such disasters occurred on the Hudson. The Hudson immunity was due to a difference in machinery. On the Mississippi "high-pressure" engines were used--there was no condenser, and the steam, which was sometimes carried at a pressure of 150 pounds to the square inch, was exhausted, after use, into the open air. When the safety-valve on such a boiler was tied down and the fire was urged until an explosion followed, the whole boat was ripped to pieces. On the Hudson condensers were used because the water was deeper and the extra weight was not of quite so much importance. Moreover, fuel was more expensive, and the low-pressure engine was more economical. Hudson River boats often reached the end of the run with boiler-plates bulging and ruined, but the heartrending disasters of the Mississippi were unknown in the East. From the Hudson the use of steam spread first to the Delaware. John Stevens, who had been associated with Livingston and Roosevelt at the end of the eighteenth century, continued his experiments after Livingston went to France as American minister. He could not find any mechanics fit to help him carry out his ideas, but he built a machine shop and trained young men for the work. In 1804 he made a number of trips on the Hudson with a 25-foot boat that was propelled by screws. He also invented the tubular boiler "which at least has been the means of working wonders, for in a boiler six feet long, four feet wide and two feet deep he exposed four hundred feet of surface, in the most advantageous manner, to the action of fire." (Macfarlane, _History of Propellers_.) In 1807, while Fulton was bringing out the _Clermont_, Stevens had a smaller, but none the less practical, boat, almost ready. He missed the honor of leading by no more than two weeks. Being unable to use her on the Hudson, Stevens, in June, 1808, sent her to the Delaware, under the command of Captain Moses Rogers, who had commanded the _Clermont_ on her first voyages, and his son, Robert L., served as engineer. Thus this vessel--she was named the _Phœnix_--was the first steamer that ever went to sea. On the Delaware the _Phœnix_ proved a commercial success. The next step in the expansion of steam navigation was taken when Nicholas J. Roosevelt built the steamer _New Orleans_ at Pittsburg (1811), and demonstrated to the incredulous frontiersmen of the region--especially to the "half horse, half alligator" keel boatmen--that a steam-driven boat could overcome the current of the swiftest part of the Mississippi.