Parties having patents or patent goods to sell, send for The National, Buffalo, N.Y., $1 per year, 10c. single copy. Back Nos., Vols., and Sets of Scientific American for sale. Address Theo. Tusch, No. 37 Park Row, New York. Mineral Collections--50 selected specimens, including gold and silver ores, $15. Orders executed on receipt of the amount. L. & J Feuchtwanger, Chemists, 55 Cedar st., New York. The Babcock & Wilcox Steam Engine received the First Premium for the Most Perfect Automatic Expansion Valve Gear, at the late Exhibition of the American Institute. Babcock, Wilcox & Co., 44 Cortlandt st., New York. For best quality Gray Iron Small Castings, plain and fancy Apply to the Whitneyville Foundery, near New Haven, Conn. Keuffel & Esser, 71 Nassau st., N.Y., the best place to get 1st-class Drawing Materials, Swiss Instruments, and Rubber Triangles and Curves. Foot Lathes--E.P. Ryder's improved--220 Center st., N.Y. Those wanting latest improved Hub and Spoke Machinery, address Kettenring, Strong & Lauster, Defiance, Ohio. For tinmans' tools, presses, etc., apply to Mays & Bliss, Brooklyn, N.Y. Mill-stone dressing diamond machine, simple, effective, durable. Also, Glazier's diamonds. John Dickinson, 64 Nassau st., New York. Send 3-cent stamp for a circular on the uses of Soluble Glass, or Silicates of Soda and Potash. Manufactured by L. & J.W. Feuchtwanger, Chemists and Drug Importers, 55 Cedar st., New York. Glynn's Anti-Incrustator for Steam Boiler--The only reliable preventative. No foaming, and does not attack metals of boiler. Liberal terms to Agents. C.D. Fredricks, 587 Broadway, New York. Cold Rolled--Shafting, piston rods, pump rods, Collins pat. double compression couplings, manufactured by Jones & Laughlins, Pittsburgh, Pa. For solid wrought-iron beams, etc., see advertisement. Address Union Iron Mille, Pittsburgh, Pa., for lithograph, etc. Machinists, boiler makers, tinners, and workers of sheet metals read advertisement of the Parker Power Presses. Diamond carbon, formed into wedge or other shapes for pointing and edging tools or cutters for drilling and working stone, etc. Send stamp for circular. John Dickinson, 64 Nassau st., New York. The paper that meets the eye of manufacturers throughout the United States--Boston Bulletin, $4.00 a year. Advertisements 17c. a line. Winans' boiler powder, 11 Wall st., N.Y., removes Incrustations without injury or foaming; 12 years in use. Beware of Imitations. * * * * * ANSWERS TO CORRESPONDENTS. _Correspondents who expect to receive answers to their letters must, in all cases, sign their names. We have a right to know those who seek information from us; besides, as sometimes happens we may prefer to address correspondents by mail.