CATALOGUES FREE TO ANY ADDRESS TOOLS OF ALL KINDS TOOLS GOODNOW & WIGHTMAN BOSTON

Smith Machine for making Thimbles or Sockets for Steam Boilers. Can make over 800 per day, all uniform in diameter and perfectly parallel, leaving no space for the bolts to bend in the thimble, making it almost impossible to make a tight boiler, for when the hydrostatic pressure is applied, straighten the bolt enough to make it leak; often has to be taken out. Address JAMES T SMITH, People's Machine & Boiler W'ks, Baltimore, Md

VENTILATION.—GREAT IMPORTance of ventilation. The vitiation of air that is constantly going on in inhabited places, exhaustion of oxygen by gas, candles and lamps. Ventilation by natural and artificial means. Contained in Scientific American Supplement, No. 525. Price 10 cents. To be had at this office and from all newsdealers.

A BIG OFFER. To introduce them, we will Give Away, 1,000 Self-Operating Washing Machines. If you want one send us your name, P. O. and express office at once. The National Co., 23 Dey St., N. Y.

VELOCITY OF ICE BOATS. A COLLECTION of interesting letters to the editor of the Scientific American on the question of the speed of ice boats, demonstrating how and why it is that these craft sail faster than the wind which propels them. Illustrated with 10 explanatory diagrams. Contained in Scientific American Supplement, No. 214. Price 10 cents. To be had at this office and from all newsdealers.

ELECTRICAL. Edward P.Thompson, Solicitor of Electrical Patents, 3 Beekman Street, N. Y. Write for testimonials and instructions.

CHLORINATION OF GOLD ORES.—A paper by G. W. Small, E.M., detailing the method of chlorinating gold adopted by the Plymouth Consolidated Gold Mining Co. Contained in Scientific American Supplement, No. 545. Price 10 cents. To be had at this office and from all newsdealers.