44 THE POPULAR SCIENCE MONTHLY. 



It is chiefly used at present in forming the longitudinal seams of 

 tubes and vessels, and in filling in blow holes and other imper- 

 fections in castings. In this latter operation additional pieces of 

 metal are fused into the openings, rendering the castings as sound 

 and good as though they had come from the mold in perfect con- 

 dition. 



A method of using the electric current, substantially the same 

 as that of Thomson, is employed by Mr. George D. Burton, and 

 shown in operation at the exhibition by the Electrical Forging 

 Company. Mr. Burton's object is not, however, to heat the metal 

 simply at the line of juncture and then complete the union of 

 the parts in one operation, but to heat a piece of metal either 

 throughout its entire length or any particular part, and then 

 forge it into shape by the hammer or special machines designed 

 to produce particular forms. He uses, as in the Thomson appa- 

 ratus, the alternating current transformed to one of great volume 

 and low voltage ; but instead of employing a number of converters, 

 each adapted to the special work in hand, he makes one large one 

 suffice, tapping this at as many points as desired. The holding 

 device for the bars to be heated consists merely of a massive pair 

 of copper clamps easily manipulated by the workman, and from 

 which the work may be quickly transferred to the anvil or shap- 

 ing machine. 



The economy in time of electric heating is very strikingly 

 shown where long bars and rods are heated. For instance, a 

 round bar of tool steel, seven eighths of an inch in diameter and 

 eleven inches long between the clamps of the machine, may be 

 brought to a welding heat in one minute by the expenditure of 

 thirty-two horse power. A bar of the same material, half an inch 

 in diameter and five inches long, requires but twenty-seven and a 

 half horse power for half a minute ; while one an inch square and 

 twelve inches long is raised to a white heat by thirty-six horse 

 power in two minutes and a half. Generally speaking, the elec- 

 tric heating may be done in a tenth of the time required by the 

 forge or furnace, and the power required is between three and 

 four horse power per cubic inch of metal heated. The feature of 

 electric heating already noticed of a bar becoming more highly 

 heated at the center than at the surface when exposed freely to 

 the air, is shown in a very convincing manner at this exhibit by 

 fusing the core of an inch bar without it losing its shape. A 

 consequence of this internal heating of a bar is the holding of its 

 heat much longer than a forge-heated one, permitting of forging 

 operations with one heat which would require two or three by 

 the old method. 



One of the most striking things in the exhibition remarkable 

 on account of being so entirely out of harmony with all our ideas 



