In 1866 he admitted to a partnership his brother, David Rau, who was with his brother seventeen years as a clerk. At the same time David's son. Robert Rau, also was admittted, and the business then took the name it has borne for more than half a century, Simon Rau & Company. Robert Rau was not only a skilled druggist, but was also a musician of high order, who both arranged and composed music. He was gifted with a fine tenor voice, and was a member of the musical organizations of the Moravian church. His literary pursuits have left various valuable papers which have been read before the Moravian Historical Society, Pennsylvania Historical Society, Pennsylvania German Society, and he was one of the founders of the Bethlehem Club. He had a very affable disposition, and in his business relations made many friends.