THK LAW OF BURNING OF MODIFIED CORDITE. 



255 



The points obtained by this calculation are shown on fig. 6. Their general 

 agreement with the measured curve is not so close as one would wish ; but for a 

 first attempt they appeared to support the idea that there are two phases in the 

 combustion of a tubular propellant : (1) when excess pressure exists inside the tube, 

 and (2) when this excess pressure disappears. Another batch, No. 97, was then tried. 

 Its time rise is shown on fig. 7. The calculation gave : 



We now have two cases of calculated internal pressure, and the next point for 

 consideration was : on what does this internal pressure depend? Looking at it from a 

 theoretical point of view, it would seem to depend on the area of the hole and the 

 length of the tube. The larger the hole the more readily can the gas get away. The 

 longer the tube, for a given hole, the more difficult will be the escape of the gas. 



In my closed-vessel experiments the cordite is cut to the internal length of the 

 vessel to avoid the wave pressures which occur if the cordite is banked up at one end. 

 The length variable does not therefore come in. 



The internal radius and pressure of the two samples were : 



Batch. 



97 



Radius of hole. 



0-04575 

 0-09003 



Internal pressure. 



4-85 

 1-93 



Now, if internal pressure varies inversely as the area of the hole, the pressure of 

 Batch 97 from Batch 88 would be given by 7^ = (x.,^) > &n &, from this, P would 



be T25 tons against 1'93 tons found by the calculation. Having regard to the great 

 variations which may be caused in my calculations by small experimental errors, this 

 result was not as discouraging as it appears on the face of it. 



