IKK LAW OF BURNING OF MODIFIED COKDITK. 



247 



tlu- quicker the time rise of pressure. In the gun, therefore, the temperature of the 

 cordite has an influence on ballistics, since at a higher temperature, the pressure 

 Ijeing raised more quickly, the projectile has less time in which to move forward ; 

 consequently there is a smaller space behind the projectile at times of equal 

 developments of gas, and higher pressures are therefore realised. Temperature, 

 therefore, is of no importance in determining the pressure-density relation, but is al'- 

 important in tin- investigation of time rises. I am not clear that other investigators 

 have borne this in mind their publications take no note of the fact. 



The pressure-density relation of M.D. cordite is shown graphically on fig. 3, and is 

 tabulated in Table A. 



Denf.il.ie:. 



Fig. 3. Pressures and densities, M.D. cordite. 

 The equation connecting the two variables is 



P = 360A-54A'+698A, 



where P is the pressure in tons on the square inch, and A is the gravimetric density 

 of loading. Since artillerists work with the Ib. as the unit of weight and the cubic 

 inch as the unit of volume, and since 1 Ib. of water occupies 2773 cubic inches at 

 60 F., density is given by the formula 2773 x weight of charge in Ibs. -r capacity in 

 cubic inches, and is then known as the gravimetric density. 



