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stopcock and into the air until all connections are thoroughly swept out with the pure gas; then turn it so that the stream is directed into the gas holder. The buoyancy of the glass causes the cylinder to rise as the gas enters.

SIMPLIFIED APPARATUS FOR DETERMINING CARBON MONOXIDE

In the apparatus shown in Figure 22 the authors have introduced two features which simplify the work of determining the amount of CO in a gas sample, an electrically heated wire-wound jacket for holding the iodine pentoxide tube and a bulb burette for measuring the sample. The tube is heated quickly. A temperature of 150° C. is satisfactory. Experiments by the authors indicate, but do not prove, that lower temperatures will suffice. The bulb burette consists of eight 100-c. c. bulbs. A narrow graduated constriction joins each bulb with the next, so that measurements can be accurately made at atmospheric pressure by means of the leveling bottle. Any number of bulbs up to eight can be used for measuring the sample.

The CO, produced is absorbed by a standard solution of barium hydroxide, and the excess is titrated with an oxalic acid solution containing 0.56325 gram per liter; 1 c. c. of barium hydroxide should equal 1 c. c. of the oxalic acid solution, and 1 c. c. of this oxalic acid solution equals 0.10 c. C. of CO at 0° C. and 760 mm. pressure.

A prepared mixture of CO and air containing 0.04 per cent of CO, as determined by a combustion analysis with the apparatus shown in Plate III, when analyzed by the iodine pentoxide method with 800 c. c. of sample, showed a CO content of 0.043, 0.043, and 0.043 per cent. The train illustrated in Figure 22 has proved ample to remove H,S, SO2, CO2, and unsaturated hydrocarbons from the gas sample before it enters the iodine pentoxide tube. Mixtures of illuminating gas and air, prepared to contain CO in known proportion, have been passed over the iodine pentoxide tube and the correct proportion of CO determined.

DESCRIPTION OF APPARATUS

The apparatus shown in Figure 22 consists in general of the bulb burette a, the purifying train b, the iodine pentoxide tube c, and the collection train d; e is a leveling bottle, and j a U tube containing pumice stone and sulphuric acid; k contains a lead acetate solution for retaining H2S if present, l contains a standard solution of barium hydrate for retaining any CO, in the sample, m contains pumice stone and sulphuric acid, n fuming sulphuric acid, o concentrated sulphuric acid, p a KOH solution, q and r concentrated sulphuric acid; & designates the furnace leads; u is a wire-wound elec

tric furnace for holding the iodine pentoxide tube; v contains a KI solution for retaining iodine; w is a standard solution of barium hydroxide for absorbing CO, produced by the reaction between the iodine pentoxide and CO; x is a guard tube containing soda lime; v is an aspirator bottle; and t is a galvanometer connected to a constantan-copper thermocouple. The thermocouple in a porcelain tube is placed inside the iodine pentoxide tube to register the temperature.

The purifying train through which the air is passed to sweep out the train after an experiment embraces y, containing a potassium hydroxide solution, and h, containing soda lime.

The authors have found that the iodine pentoxide must be purified by passing air at a temperature of 200° C. over it for several hours before determinations are made.

Later experiments performed by the authors indicate that in the afterdamp of mine explosions, in air vitiated by the firing of explosives in mines, or in air vitiated by the exhaust from gasoline locomotives, gases other than CO that reduce iodine pentoside are seldom present in large enough quantity to necessitate the use of the long purifying trains shown in the illustration. This statement refers to mixtures in which the CO is present in proportions under 0.2 per cent. In other words, the amount of other products of incomplete combustion that reduce the iodine pentoxide in the atmospheres mentioned is very much less than the amount of CO.

One column of the following table gives the CO as found by combustion analyses with the apparatus shown in Plate III. Methane and hydrogen were also present, and were determined with the CO by burning all three gases together. Another column gives the CO for the same sample, as determined by the iodine pentoxide method:

Results of two methods of analysis to determine carbon monoxide in gas samples

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In making the above analyses by the iodine pentoxide method 400 c. c. of sample was used. The purifying train consisted of four washing bottles; two contained concentrated sulphuric acid and the other two potassium hydroxide solution. One determination required about 21/2 hours.

IODINE PENTOXIDE APPARATUS USING LIQUID AIR

More recent tests by Teague 32 in connection with the investigation of the physiological effects of motor exhaust gas showed that the above method was subject to error if gasoline vapor or other heavy unsaturated-hydrocarbon vapors were present. These impurities, however, seldom exist in mine atmospheres, but when they do Teague found it necessary to purify the gases before they reached the iodine

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FIGURE 23.-Iodine pentoxide apparatus for determination of carbon monoxide, using

liquid air to remove impurities

pentoxide tube by passing them through a bath containing liquid air. Figure 23 shows a diagram of the apparatus. The iodine pentoxide tube was made of three-fourths-inch pyrex tubing 10 inches long and was filled with alternate layers of glass wool and iodine pentoxide, totaling 30 to 40 grams. The arm of the exit side of the U tube was somewhat longer than the other and tapered to make an interlock glass joint with the guard tube. A similar joint was made with the absorption bulb, thus removing the possibility of

52 Teague, M. C., The determination of carbon monoxide in air contaminated with motor exhaust gas: Jour. Ind. Eng. Chem., vol. 12, 1920, p. 964

error due to rubber connections. To condition the iodine pentoxide, raise the temperature of the bath from 220° to 230° C. for several hours, while air is drawn through. Iodine pentoxide prepared by the chloric acid (HC103) method proves more suitable and gives lower blanks than that made by the oxidation of iodine with fuming nitric acid. Barium hydroxide solutions much weaker than 0.02 N have proved undesirable, whereas 0.001 N thiosulphate could be used in the determination of the iodine liberated by the reaction, a difference which offsets the advantage of the greater amount of CO, formed. By the use of the liquid-air bath all of the CO2, water vapor, unsaturated-hydrocarbon vapors, and gasoline vapors are removed from the sample being analyzed, thus eliminating the long purifying train necessary with the apparatus described before.

DETERMINATION OF CARBON MONOXIDE BY THE PYROTANNIC

ACID METHOD

The Bureau of Mines has recently developed a new method 33 for the determination of CO in air which is based on the fact that a light brownish gray suspension is formed in a few minutes when normal blood, diluted with water, is treated with a solution of tannic and pyrogallic acids, whereas light carmine suspensions are formed in blood having CO in combination with the hæmogoblin. When compared with standards the intensity of the carmine suspension gives the percentage of saturation of the hæmogoblin in the blood used for testing. By means of suitable curves (fig. 24) the percentage of CO in the air tested can be determined.

APPARATUS NECESSARY FOR TEST

1. Set of permanent standards (Pl. VI, p. 43), made to match the color of blood having varying amounts of CO-hæmoglobin (0, 10, 20, 30 per cent, etc.), arranged in a rack with spaces between for interposing tubes of similar size containing specimens of blood for analysis.

2. Small test tubes (of the same size and glass as those used for standards) for preparing specimens of blood.

3. A dilution pipette for measuring blood. The long capillary stem is calibrated to a 0.10-c. c. mark, and the total pipette has a volume of 2 c. c., or a ratio of 1 to 20.

4. A spring hæmospast for making small puncture wounds from which the blood is obtained.

33 Sayers, R. R., Yant, W. P., and Jones, G. W. The pyrotannic acid method for the quantitative determination of carbon monoxide in blood and air : Repts. of Investigations. Serial No. 2486, Bureau of Mines, June, 1923. 6 pp. ; Tech. Paper 373, Bureau of Mines, 1925, 18 pp.

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FIGURE 24.—Curves for calculating the percentage of carbon monoxide from the percentage

of blood saturation If the percentage of oxygen is between 19 and 20.9 per cent, the volume of the sample taken for analysis is 250 c. c. or greater, and the testing is made at temperatures between 63° and 73° F. (17°-23° C.); the CO values are read directly from quadrant I. Example: Il percentage saturation is found to be 50 per cent, this value is taken on the OX axis, and the vertical line passing through this point is followed upward until it intercepts the curve, then horizontally to the left to the OY axis. The point of interception of the OY axis gives the Co (0.07 per cent).

If the sample contains less than 19 per cent oxygen, correction is made for reduced oxygen percentages by following the horizontal line through the OY axis Into the second quadrant until it intercepts the curve representing the oxygen percentage which the sample contains. The vertical line passing through this point is followed down to where it intercepts the OX axis, the interception with which gives the corrected per cent of carbon monoxide (0.06 in the above example).

If the sample used is less than 250 c. C., the vertical line is extended into the third quadrant until it intercepts the curve representing the volume of the sample taken ; then from this point the horizontal lines is followed to the right until it intercepts the OY axis, and the corrected percentage of Co is read (0.077 per cent).

If the temperature is not between 63° and 73° F., the horizontal line is extended into the fourth quadrant until it intercepts the curve representing the temperature at which the analysis was made ; then, from this point the vertical line upward is followed to the OX axis, the interception of which gives the corrected percentage of CO (0.085 per cent).

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