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SCIENCE. 



[Vol. XIII. No. 322 



done wear longer, as there is less scale on the work. Moreover, 

 the heat is uniform, and can be maintained from morning till night 

 without cessation, enabling the workmen to do more and better 

 work ; and there is no smoke, dust, or ashes. 



Fig. 2 shows the interior of a burner cylinder with oil inlet at the 

 end. The supply of oil is maintained at a constant level by means of 

 the float, which controls the oil-valve. An end view of the cylinder 



THE ELECTRIC COAL-DIGGER. 

 This is the name applied to a new mining-machine, designed 

 and constructed by Elmer A. Sperry of Chicago, and shown in 

 operation at the electrical exhibit of the National Electric Light 

 Association, during its convention in Chicago recently. For five 

 years Mr. A. L. Sweet has experimented on this project, until, with 

 the assistance of Mr. Sperry, success has crowned their efforts. 



-AERATING CYLINDER FOR DOUBLE PETROLEUM EURJJER. 



is also given, showing the burner, and the hand-wheel which 

 regulates or cuts off the supply of air and oil. The operation of the 

 mechanism is as follows : Oil is forced into the cylinder at any de- 

 sired pressure until checked by the float and valve. At the same 

 time a constant air-pressure is maintained in the cylinder by means 

 of an air-compressor, the air being admitted through the pipe at 



An electrical motor is situated on the rear of the machine, and 

 substantial gear-work transmits the power to the mechanism which 

 operates the projectile carrying the pick. 



The projectile, including the "bit," "pick," or other colter, 

 weighs from sixty pounds up, depending upon the kind of work. 

 The stroke is from six to eight inches, delivered with a force of 



THE SPERRY ELECTRIC COAL-DIGGER. 



the top of the cylinder. The hand-wheel being turned, the oil is 

 forced up through the small pipe by the air, while a certain amount 

 of air, proportioned to the oil, passes through the large pipe sur- 

 rounding the oil-pipe. At the nozzle of the burner, where igni- 

 tion takes place, the oil and air are commingled, the oil being 

 thoroughly atomized and aerated, — circumstances most favorable 

 to complete combustion. A two-burner cylinder is shown in Fig. 

 3, in which the oil inlet is at the bottom of the cylinder. 



many hundred pounds, and varying from one hundred and fifty to 

 three hundred blows per minute, according to conditions, yet al- 

 ways under control of the operator. 



The unique feature of the machine consists in the fact, that, no 

 matter where or at what point in the working stroke the projectile 

 is arrested by the work or face, it is instantly picked up at that 

 point, and returned backward to deliver another blow. For in- 

 stance : if the normal stroke is six inches, and the pick strikes the 



