Experiments upon Gunpowder. 5 



is pressed, or rather drawn into its place, and the vent 

 is closed. The stern of the valve was at first made 

 cylindrical ; but in order to make way for the priming 

 to pass down to the valve, one half of its substance 

 was taken away, as is represented in the -figure. 



When this vent is primed, the space between the 

 vent-hole and' the stem of the valve is filled with fine- 

 grained powder, and the valve is gently opened, by 

 pressing upon the end of the stem till one or more 

 grains of powder lodge themselves between the valve 

 and the aperture ; which preventing the valve from 

 closing again, a small opening is left for the passage 

 of the flame into the chamber of the piece ; when the 

 priming is lighted, the fire passing down the vent, and 

 entering the chamber, inflames the charge, and the small 

 grains of powder that were lodged between the valve 

 and the aperture being destroyed by the flame in its 

 passage through the vent, the valve immediately closes, 

 and prevents the escape of any part of the elastic fluid 

 generated by the inflammation of the powder in the 

 chamber of the piece. The pressure of this fluid upon 

 the valve assists the action of the spring, by which 

 means the valve is more expeditiously and more effectu- 

 ally closed. 



The valve was very accurately fitted to the aperture 

 by grinding them together with powdered emery and 

 afterwards polishing them one upon the other. And it 

 is very certain that no part of 'the elastic fluid made its 

 escape by this vent ; for, upon firing the piece, there was 

 only a simple flash from the explosion of the priming, 

 and no stream of fire was to be seen issuing from the 

 vent, as is always to be observed when a common vent 

 is made use of, and in all other cases where this fluid 

 finds a passage. 



