How is nitrogen estimated in a given organic compound by Duma's method?

Duma’s method: It is used for the estimation of nitrogen in all nitrogenous compounds. It consists of heating a known mass of the organic compound with an excess of copper oxide and copper in an atmosphere of carbon dioxide at about 975 K. The carbon and hydrogen are oxidised to carbon dioxide and water respectively while nitrogen is set free. If any oxide of nitrogen is produced during the process, it is reduced back to free nitrogen by passing over heated copper gauze. The nitrogen gas is collected.

over a concentrated solution of potassium hydroxide taken in a nitrometer and its volume is measured. From the volume of nitrogen collected, the percentage of nitrogen can be calculated.
Calculations
Let the mass of the organic compound taken = W g
Volume of nitrogen collected = V mL
  Atmospheric pressure  = P mm
  Room temperature  = (273 + t)K
  Aqueous tension at  = p mm
(i) To calculate the volume of nitrogen gas at NTP.