256 MAJOR J. H. MANSELL: INVESTIGATION OF 



On fig. 4 (lower curve) is shown the time rise and particulars of another batch of 

 M.D.T., No. 89. This batch was one of the exceptional batches I have previously 

 referred to, and did not show the same pressure density relation as the average run 

 of M.D. cordite. The pressure density curve for this batch is shown on fig. 3 (lower 

 curve). 



Having obtained the time rise, I tested my theories by calculating a time rise under 

 the two-phase condition I have explained. 



The internal pressure, if proportional to the inverse ratio of the area of the holes, is 

 1'896 tons, using Batch 88 as the standard. The points of this calculated time rise 

 are shown on fig. 4 (lower curve), and, except at the end of the rise, show a very close 

 agreement with the actual condition of affairs. 



The end of the rise shows disagreement. But if the actual rise of Batch 89 be 

 compared with the others, it will be seen that the falling away of Batch 89 is a most 

 exceptional condition of affairs for M.D.T. Whether the falling away was due to 

 experimental errors or to some chance peculiarity of an exceptional sample I was not 

 able to determine, as there was no more of the batch left. 



The determination of the length influence on internal pressure requires a closed 

 vessel of different dimensions, and I have not dealt with this aspect. 



From the visible behaviour of M.D.T. when burning in air it is obvious that special 

 actions are taking place. I venture to think that the calculations and experiments 

 I here set forth support the theory that in the combustion of tubular propellants 

 there are two distinct phases : the first when excess pressure exists inside the tube, 

 and the second when internal excess pressure has ceased. With such a complicated 

 problem it is clear that those investigators who have only had tubular forms of 

 propellants to deal with would be faced with a most intractable problem in 

 endeavouring to discover the true law of combustion by parallel surfaces. It is this 

 difficulty which in part accounts for the various formulas which have been advanced. 



Another somewhat important consideration is that, if you assume an equation of 

 the form S = aP" for a tubular propellaut, all tubes that have the same annulus 

 should give the same ballistics. It seems clear from experimental firings in guns that 

 the size of hole for a given annulus has an influence on ballistics. There is no 

 explanation of this fact in the simple equation formula, but it is at once explained by 

 the system of calculation which I have here set forth. The system also explains the 

 splits in the tubes and all the various phenomena connected with the combustion of 

 tubular propellants. 



At the same time it is possible to obtain also for tubes a reduction equation of the 

 form Redn. = aP + C. I originally obtained an equation of this form, which is set out 

 in Table D. By this table I am able to calculate time rises very approximately with 

 various tubes. But it is liable to break down, gives no explanation of the various 

 phenomena, and is scientifically unsatisfactory in that there is no reason why the 

 fundamental law of reduction should differ for tubes from cords. 



