nitride plus graphite material is located at the bottom end of the cylindrical charge both the plugs 106 and 108 cause increased heating at the ends of the charge so that there is a relatively uniform or 34 flat 34 temperature distribution along the length of the charge 102 the plug 108 is of slightly different material in order to facilitate free and easy movement of the plug 108 inwardly as the piston starts its upward compressive movement incidentally although a fifty fifty alloy of nickel and iron was mentioned in connection with fig1 it is preferred to use an alloy of 40 nickel and 60 iron and this would be finely powdered and mixed with graphite as included in the charge 102 of fig5 concerning dimensions it is normally desirable that the salt bushing be approximately 1 8th inch thick accordingly in fig5 if the internal diameter of the pressure chamber 26 is 3 4 of an inch then the outer diameter of the salt bushing 86 is slightly less than 3 4 of an inch and its inner diameter is approximately 1 2 inch the diameter of the stainless steel tube 104 containing the charge 102 will then be approximately 1 2 inch the piston 24 which is employed will be approximately 1 2 inch in diameter and closely fit the inside of the hole in the end load plate 82 as mentioned hereinabove with a pressure chamber diameter of approximately 3 4 of an inch the length of the pressure chamber should be approximately 6 inches similarly using.