and experimenting. Eventually, the latter pre-occupation cost him his job. One night in 1867, he was working with a lead–acid battery when he spilt sulfuric acid onto the floor. It ran between the floorboards and onto his boss's desk below. The next morning Edison was fired. His first patent was for the electric vote recorder, , which was granted on June 1, 1869. Finding little demand for the machine, Edison moved to New York City shortly thereafter. One of his mentors during those early years was a fellow telegrapher and inventor named Franklin Leonard Pope, who allowed the impoverished youth to live and work in the basement of his Elizabeth, New Jersey, home, while Edison worked for Samuel Laws at the Gold Indicator Company. Pope and Edison founded their own company in October 1869, working as electrical engineers and inventors. Edison began developing a multiplex telegraphic system, which could send two messages simultaneously, in 1874. Menlo Park laboratory (1876–1886) Research and development facility Edison's major innovation was the establishment of an industrial research lab in 1876. It was built in Menlo Park, a part of Raritan Township (now named Edison Township in his honor) in Middlesex County, New Jersey, with the funds from the sale of Edison's quadruplex telegraph. After his demonstration of the telegraph, Edison was not sure that his original plan to sell it for $4,000 to $5,000 was right, so he asked Western Union to make a bid. He was surprised to hear them offer $10,000 , which he gratefully accepted. The quadruplex telegraph was Edison's first big financial success, and Menlo Park became the first institution set up with the specific purpose of producing constant technological innovation and improvement. Edison was legally credited with most of the inventions produced there, though many employees carried out research and development under his direction. His staff was generally told to carry out his directions in conducting research, and he drove them hard to produce results. William Joseph Hammer, a consulting electrical engineer, started working for Edison and began his duties as a laboratory assistant in December 1879. He assisted in experiments on the telephone, phonograph, electric railway, iron ore separator, electric lighting, and other developing inventions. However, Hammer worked primarily on the incandescent electric lamp and was put in charge of tests and records on that device (see Hammer Historical Collection of Incandescent Electric Lamps). In 1880, he was