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Figure 16 shows the construction of the electric heater for raising the temperature of the copper oxide to 300° C. The heating element is made of 50 feet of No. 22 (B. & S. gauge) nichrome wire, wound in a helical coil. This element is easily made by using a lathe to wind the wire on a spindle three-sixteenths inch in diameter, and then coiling the helix around a grooved alundum tube of 2 inches internal diameter. Adjacent coils should be far enough apart for ample electrical insulation. Heat insulation is obtained by covering the outside of the heating element with a 1-inch layer of a mixture of magnesium oxide, asbestos fiber, and sodium silicate. The outer covering may be layers of asbestos paper or sheet metal. Close the ends with circular pieces of transite board held together by staybolts, as shown. Bring out the two ends of the wire coil to two binding posts mounted on the base of the heater. Before use, dry the furnace thoroughly for several hours at 100° C. The winding described is for use with 110-volt current, and will raise the temperature to 300° C. in 15 minutes, when a current of 1.1 amperes is used. When this temperature is attained reduce the current to about 0.7 ampere by use of a 50-ohm slide-wire rheostat. Insert a thermometer through a small hole in the top of the furnace.
TESTING APPARATUS FOR TIGHTNESS To test the apparatus for leaks, draw into the burette about 50 c. C. of air and turn cock c (fig. 10) to connect with the manifold (glass assembly through which gas is distributed to the different pipettes of the apparatus, fig. 15). Raise mercury-leveling bulb a so as to place the gas under 8 inches or more of mercury pressure. Any leaks in the stopcocks or rubber connections are shown by the mercury rising slowly in the burette. This, however, does not indicate the tightness of the rubber connections below stopcocks n, n', n", and n''. Leaks at these connections are shown by the solutions falling from marks o, 0', 0", and o'' after they have been standing a short
MEASURING THE SAMPLE
Before a series of analyses is begun adjust the gas in the compensator tube to atmospheric pressure by momentarily removing three-way cock d and compensator cock e. Adjust all the reagents in the absorption pipettes and the mercury in the combustion pipette to the marks on the capillaries. Sweep the manifold and U tube į free of oxygen or residual gas from a previous determination by drawing a sample of air into the burette and passing it into the alkaline pyrogallate pipette r to remove the oxygen. Then pass this residual nitrogen through the copper oxide tube i and pipettes p, q, and t to sweep out the remaining oxygen, which may have been contained therein. Much time can be saved by having a supply of nitrogen at hand for sweeping out the manifold and capillaries.
With the heater / raised above the copper oxide tube, switch on the current, and regulate the resistance so that the furnace will be at the desired temperature (about 300° C.) by the time the fractional combustion of the hydrogen and carbon monoxide is to be made. Turn stopcocks d, c, and b to communicate with the outside air at w. Raise leveling bulb a until the mercury reaches b. By means of a suitable capillary tube connect the sample of gas to be analyzed to the left branch of the three-way cock b and turn b to communicate with the sample. Lower leveling bulb a, drawing about 20 с. C. of gas into the burette. This sample is contaminated with air from the connections. Discard it by turning cock b to connect with w, and raise the leveling bulb a, expelling the gas at w. When the mercury reaches b, turn b to communicate again with the sample, and draw 50 to 60 с. C. of the gas into the burette as previously directed. Turn cock c through 180°, making connection with the manifold leading to the pipettes and turn b to connect with the air at w. Read the volume of gas by turning cock d through 180°, communicating with the compensator f. Raise or lower the leveling bulb a until the mercury in the compensator comes to mark f. As the burette contains a measured quantity of sample and the fluids in the pipettes have been adjusted to the marks on the capillaries, and the cocks n, n', n'', n'', j, and k closed with respect to the capillary train, the sample is ready for analyses.
CARBON DIOXIDE Raise leveling bulb a slightly to put the gas under slight pressure and avoid any possibility of pulling the caustic solution into cock n and the manifold, then turn cocks d and n to admit the sample from the burette to caustic pipette p; continue raising a until the mercury reaches d and lower the leveling bottle, drawing the gas back into the burette until the level of the caustic solution covers the glass tubes in the pipette; again pass the gas four times into the caustic pipette, and return it to the burette in the same manner. On the last pass, return the gas to the burette, bringing the level of the reagent to mark o very carefully to avoid getting any solution into the stopcock and the manifold. Close stopcock n, turn d to communicate with the compensator, and adjust the mercury level in compensator manometer to mark f. Read and record the contraction. The analyst, unless he is familiar with the gas and knows that the solution is fresh, has no assurance that all the carbon
in compensator mano, unless he is familiar with the su the carbon dioxide has been absorbed; to be certain he must pass the gas into the caustic pipette once more and note whether the volume remains constant. Any further contractions must be added to the first. If more than five passes are required to get complete absorption, the solution should be discarded and a fresh one put in the pipette.
contraction X 100 Percentage of C02=
C. c. of sample taken
UNSATURATED HYDROCARBONS OR ILLUMINANTS Pass the gas six times into the fuming sulphuric acid pipette q, then remove the SO2 fumes by passing the gas into the caustic pipette p; return the gas to the burette and read the contraction as prescribed under determination for carbon dioxide.
contraction X 100 Percentage of illuminants=
C. C. of sample taken
Ten l-mm. holes " tubing,
FIGURE 17.-Blower for combustion pipette
Pass the gas into the pyrogallate pipette r six times for low oxygen content and fresh reagent, and twelve times for high-oxygen gases. If the volume does not remain constant after 12 passes, the solution should be renewed.
contraction X 100 Percentage of oxygen=;
' c. c. of sample taken
CARBON MONOXIDE AND HYDROGEN Turn stopcocks j, k, and n' to establish communication between the burette and combustion pipette t through the copper oxide tube i; lower the furnace l over the copper oxide tube and adjust the rheostat to give a temperature of 290° to 310° C.; pass the gas slowly (10 c. c. per minute) through the copper oxide tube into pipette t and back again into the burette at the same rate; repeat.
Raise the furnace and cool the copper oxide tube by directing a stream of compressed air from a blower tube, shown in Figure 17. This tube consists of a piece of glass tubing closed at the end and bent into a one-turn coil with a number of small holes in one side of the coil. The open end is connected to one end of a compressed-air line or other source of air supply and is used for cooling the copper oxide tube and the combustion pipette by changing from one to the other as needed. Three minutes is enough for bringing the copper oxide tube back to room temperature. Return the gas to the burette and measure the contraction.
contraction X100 Percentage of hydrogen=a.
seu c. c. of sample taken
Pass the gas into caustic pipette p several times to remove the carbon dioxide. formed by combustion of the carbon monoxide, and then pass the gas through the copper oxide tube into pipettet to obtain the carbon dioxide remaining in the tube, and again pass it into the caustic pipette. Return the gas to the burette and measure the contraction. Percentage of carbon monoxider_contraction X 100
ec. c. of sample taken
METHANE AND ETHANE Store the residual gas in caustic pipette p, close cock n, and draw an excess of oxygen into the burette by way of cocks b, c, and d, connecting the oxygen supply at w. This supply may be from an “Oxone generator " or a tank of compressed oxygen; or, if the residual gas is low in combustibles, air may be used; 1 c. c. of methane requires 2 c. c. of oxygen or 9.56 c. c. of air, and 1 c. c. of ethane requires 3.5 c. c. of oxygen or 16.72 c. c. of air for complete combustion.
Measure the oxygen or air accurately and pass it into combustion pipette t, withdraw the residual gas from the caustic pipette into the burette, bringing platinum spiral s to bright-yellow heat by closing switch u and adjusting the resistance, and slowly pass the gas (10 C. c. per minute) into the combustion pipette, using all the residual gas. The rate of passing the gas can be conveniently regulated with a screw clamp on the rubber tube of the leveling bulb. When all the gas has passed out of the burette, open the screw clamp and pass the gas back and forth over the hot platinum spiral several times, and once through the copper oxide tube to sweep out the methane and ethane remaining in it. Keep the pipette cool with an air blast from the blower tube. Turn off the current, cool the pipette, and then return the gas to the burette. Measure and record the contraction as usual.
Pass the gas into the caustic pipette several times to absorb the carbon dioxide formed and again measure the contraction. To check
the completeness of combustion and remove the residual carbon dioxide left in the manifold, pass the gas once more into combustion pipette t, but quickly, because now an explosive mixture will be absent. Raise the platinum wire to the desired temperature and burn the gas again by passing it two or three times over this wire, cool the pipette, withdraw the gas into the burette, and measure the contraction as usual. If the first combustion is properly carried out, the contraction should be less than 0.2 c. C. Then absorb the carbon dioxide produced by passing into the caustic pipette and measure the contraction. Add the two contractions on burning and carbon dioxide values, and calculate the percentage of methane and ethane by the following equations:
(2x carbon dioxide formed-contraction) X 100 Percentage of ethane=1
1.5 Xc. c. of sample taken Percentage of methane= (carbon dioxide formed-2 Xethane) X 100
C. c. of sample taken Following is the result of a typical Orsat analysis: .
Typical Orsat analysis
A complete analysis by the above method takes about 1 hour; at least a third of this time is required for determining the carbon monoxide and hydrogen.
The copper oxide tube supplying the oxygen for combustion must be cooled before the paraffin hydrocarbons are burned, as those remaining in the U tube are swept out either with oxygen or air. In the reduction of the copper oxide, which occurs when carbon monoxide or hydrogen is oxidized, the oxide is reduced thus: