Crack the Nitrogen purity test valve, open the stop-cock 'G', adjust the gas flow and allow the sample gas to bubble through the purging vessel for one or two minutes. Check that the burette, the reaction chamber and the test connection tube are completely filled with water. Turn the stop-cock open to the burette connection. Then slowly open the cock 'H' to allow the oxygen to pass into the burette (not the reacting chamber), controlling the nitrogen flow. When the burette is filled below the bottom mark, close the stop - cocks 'G' and 'H' and disconnect the nitrogen sample tube , close the test valve.
Adjust the level of the gas in the burette to the 100 cc mark by holding the leveling bottle at the level of the water in the burette and carefully opening the cocks 'G' & "H' to bubble through the purging vessel to atmosphere.
1. When first passed into the burette, the Nitrogen sample will be colder than the room temperature and will expand as it warms. Therefore, the sample should be allowed to warm to room temperature for several minutes before the level is adjusted to the zero mark. Pass the gas sample into the reaction chamber by turning the burette stop cock 'H' to connect it to the reaction chamber, then raising the leveling bottle. Close the stop cock, replace the leveling bottle in the holder and allow the oxygen in the sample to react with the phosphorus. The reaction results in the emission of the white smoke consisting of phosphorus pent oxide dissolve in water to form phosphoric acid. When reaction is complete, as indicated by smoke ceasing to emit, open the cock and lower the leveling bottle to pass the unabsorbed gas from the reacting tube into the burette, pinch the rubber tube to ensure no bubbles are trapped in it. Level the liquid in the burette and the leveling bottle and note the reading indicated on the burette scale at the liquid level. This reading is equal to percentage of purity of the original Nitrogen sample.
2. The gas sample may be warm due to the reaction of the oxygen purity with phosphorus. Allow it cool to room temperature for several minutes before adjusting the level to the zero mark.