Abstract: The total nitrogen content of a given specimen is determined by sealing the specimen in conjunction with copper oxide and calcium oxide in a tube under vacuum to form a sealed specimen tube, heating the sealed specimen tube and consequently causing the specimen therein to undergo combustion and generate nitrogen, subsequently placing in a vacuumized compartment the resultant sealed specimen tube now containing the generated nitrogen, breaking the tube therein so as to liberate the nitrogen from the tube interior into the compartment and measuring the volume and pressure of the nitrogen thus released in the compartment. The heavy nitrogen content of this specimen is determined by causing a part of the released nitrogen to be collected in a separate tube connected to the compartment in which nitrogen is generated. The tube in which the nitrogen gas is collected is sealed and subsequently the heavy nitrogen concentration in the sealed nitrogen tube is measured by an ordinary method.