TESTING FOR CARBON MONOXIDE 1. M. BERKEBILE McPherson College, McPherson, Kansas
FmeumTw there will come to the chemistry departments of high schools and colleges the request for aid in determining the presence or absence of carbon monoxide in the air. Ordinarily assistance can be given in a qualitative way where the percentages are relatively high. This can be done by means of starch iodide test papers saturated with a XI08 solution in which the color change is from a white to blue color. However, there is no standard that is reliable in this case since the test is not specific for carbon monoxide. The method of determining carbon monoxide by means of absorption in a basic solution of cuprous chloride is not sensitive enough to be of help in most cases where there is a question of the carbon monoxide content. Other methods that are possible to use are frequently eliminated because of the chemicals required or the skill needed to get quantitative results. In fact, none of these methods is sensitive enough to have any advantage over such obvious indications as the odor of partially burned fuel, the physical effects upon persons or animals, or the presence of defective flues. So it is evident that if one is to be of service he must have available more precise apparatus than is commonly found in the chemistry departments. Ordinarily schools that are asked to give a service like this cannot invest in equipment to the extent that mines and other large industrial organizations do. In these organizations day after day the life of men depends upon continuous and accurate information concerning the purity of the air. In the smaller communities even the fire and, police departments find themselves hard pressed to meet the equipment needs for their primary work, and as a result lack apparatus to ascertain the presence of carbon monoxide on a quantitative basis. To many students some of the properties of carbon monoxide are common knowledge, but other i f its properties are not so commonly known. Carbon monoxide is a colorless, odorless, tasteless, nonirritating gas. It is the product of incomplete combustion, and is found in greater or lesser degree in all smoke and fumes from burning carbonaceous substances, as in stoves, furnaces, etc., and in the exhaust gases from all internal combustion engines. When inhaled, carbon monoxide is taken up by the hemoglobin. Hemoglobin's normal function is that of carrying oxygen. The hemoglobin has an affinity for carbon monoxide about 300 times greater than for oxygen; consequently, the absorption of the poisonous gas is quite rapid. As the hemoglobin becomes saturated with carbon monoxide, the oxygen in the blood stream is reduced in proportion. If the air contains sufficient carbon mon-
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Carbon Monodda Concent~ation-Hundmdthr of a Par Cent Chart I. P-ibl. Blood Saturation Vaiuee f o . a Divan Cvbon Monoxide Conc.ntrdion in the Air
oxide, death ultimately results,from oxygen starvation, but long before that point is reached, pronounced physical disturbances occur. Chart I shows the blood saturations attainable with various low concentrations of carbon monoxide, and the resultant effects on the average individual. Approximately half of the possible blood saturation is reached in the first hour of exposure, half of the remainder in the second hour, etc. It can be seen from the chart that exceedingly small amounts of gas are dangerous. A concentration of 0.02 per cent (only 2 parts in 10,000) may produce characteristic primary symptoms: headache, mental dullness, and physical inertia, in a few hours time. Unfortunately, these are very common symptoms and frequently disregarded. Chart I1 shows the importance of exposure time, in relation to the concentration of the carbon monoxide. Resuscitation measures are usually successful with victims of carbon monoxide poisoning in the advanced stages, if they have not been exposed.too long or to too great a concentration of the gas. There is no acquired or natural immunity to the gas. Repeated exposure produces identically the same effect each time. If there is any question about the presence of carbon monoxide in the home or shop, i t would be a great help to have positive tests to indicate the safety of the air. There are two practical methods. For practical use one can obtain ampoules1 which provide a dependable, inexpensive (10 to 20 cents each depending upon the usual price fluctuations), and con-
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GORDON, C. S., AND T. J. LOWE,Carbon Monoxide Detector, U. 6. Patent 1644014, October 4, 1927. Available through Mines Safety Appliance Company. Philadelphia, Pennsylvania.
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venient means of determining the presence of carbon monoxide in the air. Carbon monoxide can be determined quantitatively in concentrations ranging from 0.02 to 0.10 per cent, and higher concentrations are indicated qualitatively. The detector consists of easily crushed glass ampoule and a color comparison chart. The ampoule is a cotton-covered, thin-walled glass tube filled with a solution of palladium chloride in a water-acetone rnixture and hermetically sealed. In use, the ampoule is broken between the fingers, saturating the cotton with the solution and then suspended in the questionable atmosphere for a short period. The palladium chloride is reduced to a finely divided black precipitate of metallic palladium by the carbon monoxide. The color of the cotton is compared with the shades on the chart to determine the concentration of the gas. Probably the most practical of all the instruments available and yet within the moderate price range (around $45) is the colorimetric carbon monoxide tester using the palladium sulfateand a silico-molybdate compound.2 The indicating tube contains a yellow silica gel impregnated with the two compounds. The carbon monoxide reduces the palladium ion to free palladium which in turn reduces the higher-valenced molybdenum to molybdenum blue. In the presence of the yellow silica gel a green color is produced. The intensity of the color is proportional to the carbon monoxide concentration. A color-scale tube is mounted beside the indicating ampoule, making possible an immediate determination of the carbon monoxide. The tester is capable of indicating concentrations of carbon monoxide in the air from 0.001 to 0.10 per cent. An adsorbing chemical is used in the guard tube to remove water, gasoline 'Avdable through the Mines Safety Appliance Company, Pittaburgh, Pennsylvani~
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vapors, and other interfering substances ordinarily encountered with carbon monoxide. The tester weighs less than half a pound and the test ampoules can he stored for a year or more without deterioration. Anyone can use i t without special training. There are other methods for the detection of oarbon m ~ n o x i d ebut , ~ the two described are the cheapest and easiest to use in the hands of unspecialized persons. Those interested in knowing the details of the alarm systems, continuous recorders, and indicators for carbon monoxide gas such as those used in garages, mines tunnels, etc.. will find the material easilv ~ h t a i n e d . 4~ ? "Methods for the Detection and Determination of Carbon Monoxide," BERGER, L. B., AND H. H. SCARENK, United States Department of Interior, Bureau of Mines, Technical Paper 582. For sale by the Superintendent of Documents, Washington, D. C. Prieeis 10 cents. 'Catalogue No. 6-B, Industrial Safety Equipment, Mines Safety Appliance Company, Philadelphia, Pennsylvania.
