98 ANNUAL OF SCIENTIFIC DISCOVERY. 



"Woolwich, England, upon an iron six-pounder. The arrangement consists of 

 two pieces of brass, made to fit a groove bored in the vent-field, the vent 

 passage being between these two pieces. After the insertion of these pieces 

 of brass, they were screwed down, and on the top of them, in a line with the 

 surface of the gun, a nut was placed to hold them tight. If an enemy spiked 

 the gun in the usual manner, by removing the nut on the top by means of a 

 wrench, the vent was unscrewed, and the spike taken out. After each round 

 was fired the vent pieces were taken out, examined, and replaced ; after each 

 round the vent sank deeper into the gun. Ten rounds were fired, and after 

 the tenth a spike was driven in, which burst the vent, and the pieces of the 

 vent remained in the gun. Every time the vent was taken out previously 

 it was found to be twisted. 



Improved Bullet-mold. A patent has been recently granted to "William Aston, 

 of Middleton, Conn., for an improved bullet-mold, for casting the Minie bullet, 

 the chamber of which is a hollow cone. The object of the mold is to cast 

 such bullets with greater facility than by any of the molds heretofore used. 

 To form such bullets, the mold must be made with a core. Those now used 

 open longitudinally, and have a fixed core ; this new mold has a movable 

 core, and opens transversely. It is so made as to allow air to escape when 

 running in the molten metal, and to cut off the surplus when the mold is fulL 



A machine for making Minie balls has been recently invented by Mr. "W. 

 A. Sweet, of Syracuse, N. Y. These bullets differ from the common round 

 bullet in being of a conical shape with a cavity in the base. Hitherto they 

 have been invariably cast in molds in the same manner that the common 

 bullet is cast, by which process it is impossible to make balls of equal weight 

 or free from imperfections, which faults, as they exist in a greater or less 

 degree, affect the accuracy of the rifle. The machine is comprised within a 

 space of a foot square, and weighs about 65 pounds. There are no springs or 

 cogs in it, and there is very little liability of its getting out of order. The 

 bars of lead, rolled to a proper thickness, are fed into a hopper and run under 

 a die which "swedges" out the bullet, and at the same instant the cavity is 

 pressed into the base ; the bullet is discharged from the die, which again re- 

 ceives the bar and repeats the process. The machine thus makes two bullets 

 a second, or 120 a minute, and is capable of even faster work. 



DIFFICULTIES ATTENDING THE CONSTRUCTION OF LAKGE 



OKDNANCE. 



During the past year, Mr. Nasmyth, the well-known English mechanician, 

 constructed for the British Government an immense experimental gun of 

 wrought iron, the weight of which with its carriage was intended to be 50 

 tons. It was also expected to throw a solid shot of half-a-ton weight four 

 miles with a charge of 225 Ibs. of powder. In manufacturing this immense 

 piece of ordnance, it was found that the thickness of the mass so retarded the 

 cooling gained by successive heatings, that portions of the metal assumed a 

 crystalline form, and weakened the whole to such an extent that its use was 

 considered impracticable, This fact has attracted considerable attention in 



