NOVEMBER 15,1940
ANALYTICAL EDITION
that, by increasing the amount of the mixture, analysis could be made where a component is present in less than this amount. None of the binary mixtures was particularly difficult to separate. With the three-component mixture, methyl myristate, methyl palmitate, and methyl stearate, it was difficult to obtain a flat for the methyl palmitate. The results given, however, check fairly close to the actual composition of the mixture. The mixture of methyl laurate, methyl myristate, and methyl palmitate was satisfactorily separated on the first fractionation. Only one four-component mixture was fractionated. V i t h this mixture the operator did not know which esters were present. The first fractionation, represented in Figure 5 (upper), served as a guide for the second fractionation shown in Figure 5 (lower). The first fractionation gave a flat for methyl caprate, methyl myristate, and methyl stearate and also a n indication that some methyl palmitate was present. The second fractionation gave a flat for methyl myristate, methyl palmitate, and methyl stearate. Combining the two fractionations it was evident that the mixture contained all tour esters. The analysis was calculated on the second fiactionation because it was believed that some of the lowlmiling methyl caprate was lost through the condenser a t the head of the column on the first fractionation. Although there was some loss of caprate in the second fractionation, it was not so great as that in the first. The saponification cquiralent of the mixture as calculated from the actual com-
661
position w s 285.6, and from the composition determined experimentally i t was 287.8.
Summary The methyl esters of caprylic, capric, lauric, myristic, palmitic, and stearic acids have been purified and their refractive indices determined. Small quantities of known mixtures of these esters have been fractionally distilled through a spinning-band column and their composition has been determined. K i t h the exception of the more volatile esters the analyses are fairly accurate, considering the difficulty connected with separating such mixtures. I n oil analyses where only >mall quantities of these acids are availalde this method offers for the first time a convenient and fairly accurate method of analysis.
Literature Cited (1) Armstrong, E. F., Allan, J., and Moore, C. W., J . SOC.Chem. Ind., 44, 63T (1925). (2) Elsdon, G. D., Analyst, 38, 8 (1913). (3) Haller, hl., Compt. rend., 146, 250 (1908). (4) Hilditch, T. P., “Fats and Waxes”, New York, D. Van Nostrand Co., 1927. (5) Lepkovsky, S. L., Feskov, G. V., and Evans, H. M., J . Am Chem. Soc., 58, 978 (1928). (6) Lesesne, S.D., and Lochte, H. L., IND. ENO.CHEM.,Anal. Ed., 10.450 (19381. (7) Uno; S.,And Iwai, M., J . SOC.Chem. I d . Japan, 38, Suppl. bind., 603 (1935).
Determination of Carbon Monoxide Pyrogallic-Tannic Acid Method as Adapted to Standard Gas Analysis Equipment FRED COOK, Bituminous Casualty Corporation, Rock Island, Ill.
-4method is described for the determination of carbon monoxide in concentrations of 0.10 to 0.002 per cent. The apparatus is designed as an accessory to standard gas analysis equipment and requires a special set of color standards in addition to regularly available laboratory devices. The determination may be run either independently or simultaneously with other gas analysis. ITH ordinary gas analysis apparatus the lower limit of concentration that may be measured v i t h certainty is 0.1 per cent. I n the case of carbon monoxide this limit is not low enough to detect quantities that are dangerous to health, to permit folloving the progress of mine fires in sealed sections to their extinction, or to ensure the absence of carbon monoxide in industrial gases where small quantities of this substance are undesirable. The device described here is essentially the “pyro-tannic acid method” for determination of carbon monoxide in air as described by Sayers and ”ant (1) in 1927, incorporated as an accessory to standard gas analysis equipment. Several advantages are obtained by this modification. The method of Sayers and T a n t is based on the formation of a stable colored suspension by the addition of a small amount of pyro-tannic (equal parts of pyrogallic and tannic)
acid to a water-blood solution which has been partly or completely saturated with carbon monoxide. The procedure recommended involves collecting a 250-cc. sample of carbon monoxide-contaminated air through a soda-lime tube into a dry sample bottle. A small quantity of 20 to 1 blood solution is added to the bottle and shaken for 20 minutes to ensure equilibrium. The solution is transferred to a small tube, pyro-tannic acid added, and the blood saturation measured by comparison with color standards. The amount of carbon monoxide in the air is calculated from the blood saturation and the oxygen content of the air. This method is very well suited for field work where on-thespot information is desired as to the presence of small quantities of carbon monoxide in air that is known to contain between 19 and 21 per cent of oxygen. The method was devised as a test of the purity of air to be used for breathing and the authors claim a n accuracy of 0.005 to 0.030 per cent in concentrations of 0.010 to 0.200 per cent of carbon monoxide. Work in the writer’s laboratory corroborates this accuracy. For general application in laboratory gas analysis this procedure is objectionable because the sample must be collected in a dry bottle of limited size. The sample is rendered unfit for analysis of other gases by the necessity of opening the bottle in the laboratory, and the oxygen content of the sample must be known within reasonable limits. An inspection of Equation 2 will illustrate the importance of accurate data on the oxygen content. When used with the device described here a sample collected by any method, wet or dry, is satisfactory About a 100-cc. portion is needed for the carbon monoxide analysis,
INDUSTRIAL AND ENGINEERING CHEMISTRY
662
and any additional amount may be used for other analysis. While the lower limit that may be measured in air containing 21 per cent of oxygen is 0.007 per cent, if the oxygen is reduced to 6 per cent b y partial absorption, as little as 0.002 per cent of carbon monoxide may be detected.
gram) may be blown from 3-mm. glass tubing. Color standards in steps of 10 per cent blood saturation may be prepared from pigments by comparison with blood saturated with air-carbon monoxide mixtures of known concentration, or a set may be purchased (Mine Safety Appliances Co., Pittsburgh, Penna.) .
Apparatus The apparatus is connected through capillary tubing to the manifold of a gas analysis apparatus. The only available outlet on the manifold may be the intake port and Figure 1 shows a convenient arrangement for connecting the apparatus to the intake port. The details are essentially as illustrated.
VOL. 12, NO. 11
3Iethod of Operation The gas sainple to be analyzed is drawn into the buret of the apparatus. If hydrogen cyanide or hydrogen sulfide is present, it must be removed in the caustic pipet, as these gases interfere with the color of the blood solution. The sample is then transferred into the sample reservoir, as shown in Figure 1, 2 cc. of 20 to 1 blood solution are added to absorber, and the sample is slowly bubbled through the solution. I t requires about 15 minutes to pass the sample through the absorber and this time may be used for the analysis of other constituents of the gas mixture; information on the oxygen content is needed for the calculations. After the gas has been passed through the absorber, the blood solution is transferred to a 3-cc. test tube, 0.04 gram of pyrotannic acid is added, and the mixture is shaken and allowd to stand for 30 minutes, at which time it is compared with the color standards. It is convenient to make up a blank from unsaturated blood solution to use as a check for zero saturation. I t may be necessary to add or remove oxygen from the gas sample in order to change the sensitivity range of the analysis. Normal air (21 per cent oxygen) is suitable for concentrations of carbon monoxide between 0.008 and 0.1 per cent. Between 0.01 and 0.002 per cent it is necessary to reduce the oxygen to G per cent by partial absorption in the alkaline pyrogallic acid pipet. For this purpose only fresh pyrogallic solution should be used, as after absorbing oxygen the solution gives off traces of carbon monoxide that may interfere with the results. Table I illustrates the accuracy of the method and the effect of reducing the oxygen content of the sample. TABLE I. co
from Gas Volumes
SECOTFIONI
ABSOR BE R
I1 FIGURE I
The large bottle forms a reservoir for the gas sample by displacing its contents of acidified water into the leveling bulb as the sample is transferred to the bottle from the Orsat buret. The leveling bulb is mounted on a vertical rod, so that it may be lowered if necessary to facilitate the transfer of the sample into a bottle, and an adjustment of its height is helpful in regulating the rate of passing the sample through the absorption cell. A section of the absorption cell is shown. It consists of a 15-em. (Ginch) length of 8-mm. glass tubing with a 2.5-cm. (1-inch) bulb blown just one side of center. The bulb is necessary to prevent loss of solution due to foaming; it may be necessary to wax the interior of the bulb for the same purpose. This absorption cell is joined by a piece of rubber tubing (at B ) to a short length of glass tubing that has a sintered glass disk fused into the top. This disk should be of porosity that will pass the sample under a head of several feet of water but will not pass the solution as it stands in the absorber. The unit is joined by a second piece of rubber tubing (at A ) to the sample reservoir. Beef blood is satisfactory for the analysis and is available
at packing houses and butcher shops. If desired, blood of guinea pigs, white rats, or humans may be substituted. A quantity of blood, prevented from coagulating by the addition of a pinch of potassium citrate, may be preserved for several weeks in a refrigerator. The 20 to 1 water-blood solution that is used in the test will keep only a few days at room temperature. Pyro-tannic acid is prepared by grinding in a mortar equal weights of pyrogallic and tannic acids. A small spoon for adding the pyro-tannic acid (about 0.04
CoMPARISoN O F RESULTS Oa co in Found by hlixture Analysis Deviations
70
%
%
%
0.10 0 05 0.025
21 21 21 12 21 12 21 12
0.11 0.016 0 030 0.025 0.007 0.010 0.00
0.01 0.004 0,005 0.000 0.003 0,000 0.003 0.001
12
0 000
0.025 0,010 0.010 0.005 0.005 0.005 0,002 0.002
6
6
0.004 0.005
0.002
0.000 0.00% 0.000
Calculations are based on the fact t h a t the affinity of carbon monoxide for the hemoglobin of the blood is 300 times that of oxygen, At equilibrium the expression may b e written: PO2 X HbCO _ -300 PCOX HbOz 1 or yo€IbCO %OZ % co = 100-70 HbCO 300
It is obvious that lowering the percentage of oxygen in the mixture reduces the lower limit of carbon monoxide that may be determined. This may be carried only so far as the amount of carbon monoxide in the sample is sufficient t o produce saturation of the blood solution a t equilibrium. The amount of blood used in the test (0.1 cc.) requires 0.0185 cc. of carbon monoxide for 100 per cent saturation. The lower limit of blood saturation that can be detected is 10 per cent. This limits to about 0.002 per cent the carbon monoxide that may be determined in a 100-cc. sample. Literature Cited (1) Sayers, R. R., and Yant, W. P., Bur. Mines, Tech. Paper 373 (1927).
