In the District of Columbia many “were superior mechanics.” Olmsted, in his journeys through the slave states just before the Civil War, found slave artisans in all the states. In Virginia they worked in tobacco factories, ran steamboats, made barrels, etc. On a South Carolina plantation he was told by the master that the Negro mechanic “exercised as much skill and ingenuity as the ordinary mechanics that he was used to employ in New England.” In Charleston and some other places they were employed in cotton factories. In Alabama he saw a black carpenter—careful and accurate calculator and excellent workman; he was bought for $2,000. In Louisiana he was told that master mechanics often bought up slave mechanics and acted as contractors. In Kentucky the slaves worked in factories for hemp-bagging, and in iron work on the Cumberland river, and also in tobacco factories. In the newspapers advertisements for runaway mechanics were often seen, as, for instance a blacksmith in Texas, “very smart”; a mason in Virginia, etc. In Mobile an advertisement read “good blacksmiths and horseshoers for sale on reasonable terms.”[65] Such men naturally showed inventive genius, here and there. There is a strong claim that the real credit for the invention of the cotton gin is due to a Negro on the plantation where Eli Whitney worked. Negroes early invented devices for handling sails, corn harvesters, and an evaporating pan for refining sugar. In the United States patent office there is a record of 1500 inventions made by Negroes and this is only a part of those that should be credited to Negroes as the race of the inventor is not usually recorded. In 1846 Norbert Rillieux, a colored man of Louisiana, invented and patented a Vacuum pan which revolutionized the method of refining sugar. He was a machinist and engineer of fine reputation, and devised a system of sewerage for New Orleans which the city refused to accept because of his color. Sydney W. Winslow, president of the United Shoe Machinery Company, laid the foundation of his great organization by the purchase of an invention by a native of Dutch Guiana named Jan E. Matzeliger. Matzeliger was the son of a Negro woman and her husband, a Dutch engineer. He came to America as a young man and worked as a cobbler in Philadelphia and Lynn. He died in 1889 before he had realized the value of his invention.