At this time something happened which did much to change his whole life. Through the interest of his superintendent it became possible for him to purchase ten shares in The Adams Express Company for five hundred dollars. Andrew's business instinct led him to see that it was a splendid opportunity, and his mother was just as anxious as he was to make the venture. After a consultation they decided to mortgage their little home and buy the shares. This little transaction was destined to be the forerunner of many successful business deals. One day, while he was travelling on the railway, a man showed him the model of a sleeping-car. Such things were at that time unknown, but Andrew saw instantly that the invention was a good one, and made arrangements for the inventor to meet the superintendent of the railroad. The outcome was that a company was formed to build sleeping-cars, and Andrew Carnegie was one of the number. Soon after this he was made superintendent of the Pittsburgh division of the Pennsylvania Railroad. Not long after he was promoted to this position the company began to make experiments with an iron bridge. Up to this time all bridges had been built of wood. The experiments with iron proved successful. There had been so much delay on the railways by the bridges being broken or burned that the cast-iron bridges were welcomed. Mr. Carnegie, with his keen business instinct, saw at once that iron bridges must displace the wooden ones. He formed a syndicate known as The Keystone Bridge Works, and his first undertaking was to build a bridge with a span of three hundred feet over the Ohio River. Thus began the work of iron and steel constructions which Mr. Carnegie followed up until he became known throughout the world as the "Steel King." Before many years had passed Mr. Carnegie not only owned his own immense iron and steel works, but also a fleet of steamers which were used to transport the iron ore across the Great Lakes. He built his own railroad to convey the ore from the lake ports to Pittsburgh, a distance of 425 miles. In 1900 The Carnegie Steel Company was organized with a capital of one hundred million dollars. The enormous concern gave employment to 45,000 people. One of the plants alone covers an area of seventy-five acres. It is no exaggeration to say that it is by far the greatest manufacturing concern of its kind in the world. When Mr. Carnegie decided to retire he sold out his interest in the steel works for two hundred and fifty million dollars. It was said at that time that he could give away thirty-five thousand dollars a day and never touch his capital. For many years he gave large sums of money for public libraries and other enterprises which seemed to him to be deserving of assistance.