Chemical lecture experiments . p. 26 ; potassium pyrogallate solution. 10. Quantitative determination of nitrogen in air. — Whilethe combination of burning phosphorus and oxygen attendedby light and,heat is extremely rapid, the elements do, never-theless, unite at ordinary temperatures. ATMOSPHERIC AIR 187 One hundred cubic centimeters of air are introduced intoa eudiometer tube. A stick of phosphorus 3 or 4 cm. longis carefully cleaned under water and fastened to a piece ofcopper wire. The phosphorus is then thrust under themouth of the eudiometer tube, whichremains under water and is pushed
Chemical lecture experiments . p. 26 ; potassium pyrogallate solution. 10. Quantitative determination of nitrogen in air. — Whilethe combination of burning phosphorus and oxygen attendedby light and,heat is extremely rapid, the elements do, never-theless, unite at ordinary temperatures. ATMOSPHERIC AIR 187 One hundred cubic centimeters of air are introduced intoa eudiometer tube. A stick of phosphorus 3 or 4 cm. longis carefully cleaned under water and fastened to a piece ofcopper wire. The phosphorus is then thrust under themouth of the eudiometer tube, whichremains under water and is pushed aconsiderable distance up the tube, intothe air. The copper wire is then bentso as to rest on the bottom of the dishand support the phosphorus in the air(Fig. 81). The level of the water in thetube will, of course, be depressed by asmuch as the volume of the copper andthe phosphorus introduced. Hence it isimportant that the eudiometer be of suffi-cient size to allow of this expansion overthe 100 cc. After the whole apparatus. has stood over night it will be found Fig. 81 that a diminution in volume has takenplace. By withdrawing the phosphorus and reading off thevolume of the residual gas it will be found to be approxi-mately 80 cc, , four-fifths of the original volume. In case a graduated tube is not at hand a linear measure-ment of the diminution may be made. Eudiometer tube 2 cm. in diameter ; meter stick ; P ; Cu wire. 11. Quantitative absorption of oxygen from air by metalliccopper. — By measuring the quantity of air passed over aheated copper coil and the amount of gas collected at thepneumatic trough, the proportion of oxygen and nitrogenpresent in the air may be quantitatively determined. A stoppered cylinder is fitted with a two-holed rubber stop-per carrying one tube leading to the bottom of the cylinderand a glass elbow directly connected with the combustion-tube 188 CHEMICAL LECTUKE EXPERIMENTS containing the copper coil. Connection is then made with afaucet
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