ELECTRICAL APPARATUS. 295 



instrument shows the passage of the fluid during the charg- 

 ing of the bottle. The coating both inside and outside is 

 put on as represented. The belt on the outside is only 

 put in contact with the lower part of the coating by means 

 of the sliding piece on the outside. The wire within is at- 

 tached to the inside of the bottom. In charging, the lower 

 part becomes charged first, and the fluid will be seen to pass 

 upwards inside in flashes, w r hile if the connecting piece be 

 withdrawn, the fluid will be seen to pass downwards on the 

 outside from the belt to the lower part. Price, $3.00. 



The Electrical Cannon. Fig. 343. 



(Fig. 343.) This is a brass 

 cannon, about five inches long 

 and one inch in diameter, 

 mounted on a wooden stock ; 

 the ball at the top has a 

 wire attached to it, which passes down a short tube of ivory 

 into the chamber of the cannon, to within an eighth of an 

 inch of the opposite side, and through this space the spark 

 passes to explode the gas, which may be formed by putting 

 a handful of iron nails, or the same quantity of pieces of 

 zinc, into a wine bottle ; to these add half a pint of water and 

 a wine glass full of sulphuric acid. Have ready prepared 

 for the bottle a cork which fits it, and through which the stem 

 of a tobacco pipe passes. The mixture will soon throw up 

 bubbles of gas ; when it is supposed that these have dis- 

 placed the air of the phial, cork it up, so as to suffer the 

 gas to pass out only through the stem of the pipe. Here it 

 may be collected in a collapsed bladder fastened to the 

 other end of the stem, or, if preferred, the bladder may be 

 tied to the top of the cork itself. The gas will soon fill the 

 bladder. When enough for use has been collected, the stem 

 may be broken, so as to separate the bladder and the bottle ; 

 then holding the cannon with the mouth down, press the 

 gas into the cannon, which, by its levity, will partially dis- 

 place the atmospheric air, mixing therewith, and producing 

 an explosion when the spark is passed through. The mouth 

 of the cannon must be well corked to prevent the escape of 

 the gas previous to firing. Price, $2.00. 



