Document NGE9wD3awVdxYoMaz4KQ5p7Yb

American Society of Heating and Ventilating Engineers Guide, 1934 become thoroughly frozen the wet-bulb temperature will rise .to normal. Care must be taken to read the temperatures in the region below 32 F accurately because the spread between the wet- and dry-bulb is small. In taking humidity readings in ducts it is usually impracticable to use a sling psychrometer. For this work the stationary hygrodeik arranged for bolting on to the side of the duct, with two bulbs extending into the duct, will be found very convenient. Due to the velocity of the air passing over the bulbs within the duct an accurate reading will be secured, corresponding to that given by the sling psychrometer. CARBON DIOXIDE DETERMINATION*3 4 * At ordinary concentrations carbon dioxide is not harmful. The amount of carbon dioxide in the air is a convenient index of the rate of air supply, and of the distribution of the air within rooms. A high carbon dioxide concentration in parts of an occupied room may indicate air stagnation which can result in objectionable odors or in failure to remove local surplus heat. The Petterson-Palmquist apparatus has been generally accepted as the standard device for the determination of carbon dioxide in air investiga tions. The principle involved is the measurement of a given volume of air, the absorption of the contained carbon dioxide in a caustic potash solution, and the remeasurement of the volume of air at the original pressure in a finely graduated capillary tube, the difference in volume representing the absorbed carbon dioxide. (See Report, of Committee on Standard Methods for Examination of Air, American Public Health Asso ciation, Vol. 7, No. 1; American Journal of Public Health, Jan., 1917). Where field conditions are such that this apparatus may not be con veniently used, as in street cars, air samples may be collected in prepared bottles having rubber stoppers, and these may be subjected to laboratory analysis. DUST DETERMINATION Many laboratory methods have been developed to measure the dust in the air. These involve the collection of dust on sticky plates, on filter paper, in water, on porous crucibles, or by electric precipitation, and the subsequent determination of the amount of dust by microscopic counting, weighing, or titration. While there is no standard method, the Hill dust counter, using a microscope, the impingerV using chemical changes in water, and the Lewis sampling tube6, involving the analytical weighing of a porous crucible, are accepted. FLUE CAS ANALYSIS The analysis of flue gases by chemical means is made with the Orsat apparatus. A solution of KOH is used to absorb the C02. Free oxygen is See A.S.H.V.E. research paper entitled Indices of Air Change and Air Distribution, by F. C. Houghten and J. L. Blackshaw (A.S.H.V.E. Journal Section, Heating, Piping and Air Conditioning, June, 1933). . 4Public Health Bulletin, No. 144, 1925. U. S. Public Health Service. Testing and Rating of Air Cleaning Devices Used for General Ventilation Work, by Samuel R. Lewis (A.S.H.V.E. Journal Section, Heating, Piping and Air Conditioning, May, 1933). 574 Chapter 40--Test Methods and Instruments absorbed by a mixture of pyrogallic acid and KOH. The solution for absorbing the CO is cuprous chloride. The apparatus consists of a burette surrounded by a water jacket, to receive and measure the volume of gas. The burette is connected by a manifold of glass to pipettes con taining liquids for absorbing C02, 02 and CO. MEASUREMENT OF SMOKE DENSITY Smoke density is usually measured by comparison with the Ringel mann Chart (Fig. 1). In making observations of the smoke issuing from a chimney, four cards ruled like those in Fig. 1, together with a card printed in solid black and another left entirely white, are placed in a horizontal row and hung at a point 50 ft from the observer and as nearly as convenient in .line with the chimney. At this distance, the lines become invisible, and the cards appear to be of different shades of gray, Fig. 1. Ringelmann Smoke Chart ranging from very light gray to almost black. The observer glances from the smoke coming from the chimney to the cards, which are numbered from 0 to 5, determines which card most nearly corresponds with the color of the smoke, and makes a record accordingly, noting the time. Observations are made continuously during say one minute, and the estimated average density during that minute recorded, and so on, records being made once every minute. The average of all the records made during a boiler test.is taken as the average figure for the smoke density during the test, and the entire record is plotted on cross section paper in order to show how the smoke varied in density from time to time. Smoke Recorders Smoke recorders are available which give a much more accurate in dication of the amount of smoke being produced than the Ringelmann Chart. Although most of these instruments are in the process of develop ment, they constitute a satisfactory tool in the control of smoke emission. They all depend upon projecting a beam of light through the smoke flue or through a separate compartment from which a sample of the flue gas is drawn continuously. The light of the beam which passes through with out being absorbed by the smoke is measured to determine the smoke 575