tender for calibration gas mixture with pressure gauge, valve and septum (1/8 inch) in 0.5 ltrs aluminiumcanister, with filling pressure 20 kg per cm sq with following gases: 1)acetylene: 500 ppm, 2) carbondioxide:500 ppm, 3) carbon monoxide: 500 ppm, 4) ethane: 500 ppm, 5) ethylene: 500 ppm, 6) hydrogen: 500 ppm,7) methane: 500 ppm and 8) nitrogen balance.