And so, one after another, various useful additions came into existence, until we have the modern paper-machine, which differs mainly in width, length and productive power from the machines of the thirties. In the meantime, researches for new paper-making materials had been in progress. As early as 1719, Reamur, observing how wasps made their nests from wood, threw out the hint to paper-makers, but for over a century there was no important result. In 1727, Dr. Brueckmann, a German naturalist, published a work on stones, four copies of which are said to have been printed on paper made with asbestos. In 1751 M. Guettard in France published his experiments and showed samples of paper made from bark, leaves and wood; while in 1765 Jacob Christian Schaffers, of Ratisbon, published a volume, a copy of which exists in the Smithsonian Library, upon the different sorts of paper he could make without rags.[A] [A] A copy of the second edition of this work is in the Library of the University of Michigan at Ann Arbor. Matthias Koops in 1801 printed some account of his patents for utilizing waste papers, straw and wood. This volume, printed on straw paper, with one signature on paper claimed to be made of wood, is well worth reading, and is to be found both in the Boston Public Library and in the Harvard College Library, and quite likely elsewhere. These experiments are only interesting as forerunners. In their own time they came to naught. Not until 1840 was ground wood-pulp invented by Keller. The production of cellulose from straw and esparto by the soda process was discovered by Routledge, an Englishman, in 1860, while the first patents for making wood soda pulp were those of Watt and Burgess in 1854. To an American belongs the credit for the important invention of the sulphite process, Benjamin C. Tilghmann, of Manayunk, Pennsylvania, having taken out the first patents in 1866. Although excellent fiber was obtained, the engineering difficulties proved so serious that experiments were temporarily abandoned in the United States. But the process was afterward put upon a successful commercial basis by Fry and Ekman, at Berzwik, Sweden, in 1870. Americans soon took up the problem with renewed energy, and the late Charles S. Wheelwright, of Providence, Rhode Island, after a visit to Sweden in 1882 on which he obtained the rights to the Ekman patents, introduced the process at the plant of the Richmond Paper Company, in Providence, and while a commercial success was not realized, it was an important step in the development of the industry, and not many years passed before the United States gained a leading position in the production of wood-pulps.[B] [B] See Little & Griffin, “The Chemistry of Paper-making.” Thus in less than ninety years, from Robert’s invention of 1798 to the early eighties, the world witnessed a complete revolution of the paper industry, which had struggled along in the same old rut for some two thousand years.