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1258 CHAPTER 52 1958 Guide lurer& by R. N. St. John. A glass rod is interposed between a light source and a photo-sensitive cell, both before and after being exposed to the flue gases from a heating device. The diminution of the light transmitted by the rod, due to the deposit of soot on its surface, causes a reduction in the cell emf which is taken as an index of the concentration of smoke in the flue gases. A description of the method is contained in National Bureau of Standards Commercial Standard CS104-46.67 DETERMINATION OF AIR CONTAMINANTS Two measures of air dustiness are in use: particles per unit volume of air, and weight per unit volume of air. A comparative method consists in drawing known samples of air through a known area of filter cloth or paper, and comparing the density of the resulting spots with blackness charts or with spots from other sources. For counting, particles are captured in a device such as. the SmithGreenburg impinger, the Owens jet dust counter, or in an electrostatic or a thermal precipitation device designed for the purpose.62 Counting is done with a microscope, and the method yields important results when the nature or constituents of the dust are of interest. For a weight determination, a known volume of air is drawn through a porous crucible or thimble, and the weight gained by the thimble during the operation is the weight of the dust captured from the air sample.63 For precise work, the thimble must be dried in a desiccating chamber before weighing each time. At the National Bureau of Standards a test method was developed for interested Government agencies, under which measured samples of the un cleaned air and of the air cleaned by a device under test are passed through filter papers.66 The ratio of the flow rates through the two filter papers is adjusted during successive tests, until the resulting dust spots approach equality in density as shown by a photometer. The ratio of the flow rates is then indicative of the effectiveness of the cleaner in arresting dust. A statement of an air cleaner's efficiency by any test method, is meaningless unless the test dust is specified. Other instruments for determining gaseous and particulate air contaminants are described in industrial hygiene litera- tUTG 62,-65t 66, 67 SOUND AND VIBRATION MEASUREMENTS Approximate measurements of sound intensity can be made by aural methods. The ear is used to compare the measured noise with sounds of known strength. Electrical devices, in which the ear plays no part, furnish the most satis factory means of measuring noise intensities. The sound meter consists essentially of a microphone coupled to an amplifier designed with an ear-like response. The output of the microphone is read on a sensitive direct current milliammeter graduated to read directly in decibels. Instruments of this type, if connected with suitable band pass filters, can be used to study the intensity of the sound over its entire range of frequencies. Electrical instruments are available for measuring the frequency, ampli tude and acceleration of a vibrating mass. They are usually more con venient and accurate than the vibrating reed tachometer, the seismic type displacement meters or the accelerometers which. can also be used for this purpose. Sound level meters are discussed in several text books68 and standards.70 Instruments and Measurements 1259 REFERENCES i Standard Code for.Testing and Rating Steam Unit Heaters (adopted jointly by The American Society op Heating and Ventilating Engineers and the Industrial Unit Beater Association, January 1950, second edition). *A.S.H.V.E. Standard Code for Testing and Rating Steam Unit Ventilators (A.S.H.V.E. Transactions, Vol. 38, 1932, p. 25), adopted June, 1932. * A.S.R.E. Standard Methods of Rating and Testing Air Conditioning Equipment, A.S.R.E.'Circular No. 13. A Survey of Testing Methods and Rating Limits for Domestic Heating Devices, by R. S. Dill (A.S.H.VJB. Transactions, Vol. 51, 1945, p. 185). s For a comprehensive treatment of temperature measurement the reader is referred to Temperature, Its Measurement and Control in Science and Industry, a symposium sponsored by the American Institute of Physics and published by Reinhold Publishing Corp. * Temperature Measurement in Engineering, by H. D. Baker, E. A. Ryder, and N. H. Baker (John Wiley and Sons, New York). ' Temperature Measurement (A.S.M.E. Power Test Code, Part 3). * Errora in the Measurement of the Temperature of Flue Gases, by P. Nichollsand W. E. Rice (A.S.H.V.E. Transactions, Vol. 35, 1929, p. 473). * Investigation of Warm Air Furnaces and Heating Systems, by A. C. Willard, A. P. Kratz and V. S. Day (Illinois Engineering Experiment Station, Bulletin No. 120). 10 Measuring Heat Transmission in Building Structures and a Heat Transmission Meter, by P. Nicholls (A.S.H.V.E. Transactions, Vol. 30, 1924, p. 94). "Parallel-connected Thermocouples for the Testing of Gas Appliances, by Walter B. Kirk and George J. Pacanovsky (Gas, September, 1939, p. 51). "American Standard for Indicating Pressure and Vacuum Gages, Round Dial Type, with Elastic Pres sure Chamber. B. 40.1-1939-(Ameriean Standards Association). "Standard Test Code for Centrifugal and Axial Fans, 1938 (A.S.H.V.E. and N.A.F.M.) published by NA..F.M. as Bulletin No. 110. 14 Fan Engineering, Buffalo Forge Company, 5th Edition, p. 165. 11 Illinois Micromanometer ( University ofIllinois, Engineering Experiment Station Bulletin No. 120, p. 91). 14 The Weathertightness of Rolled Steel Windows, by J. E. Emswiler and W. C. Randall (A.S.H.V.E. Transactions, Vol. 34, 1928, p. 527). 17 Pressure Measurement (A.SJd.E. Power Test Code 1936, Part 2, Chapter 2). u The Measurement of Static Pressure, by C. J. Fechheimer (Mechanical Engineering, August, 1927). J* Psychrometric Tables for Vapor Pressure, Relative Humidity and Temperatures of the Dew-Point (U. S. Department of Agriculture, Weather Bureau, Washington, D. C.). 10 For technical data refer to Fluid Meter Reports, Parts 1--1937, 2--1931, and 3--1933 (American Society of Mechanical Engineers). 71 Technical Notes No. 546 (National Advisory Committee for Aeronautics, November, 1935). 11 The Characteristics of Double Pitot Tubes, by F. R. Ingram, E. Diez-Canseco and L. Silverman (A.S.H.V.E. Journal Section, Heating, Piping and Air Conditioning, November, 1942, p. 708). Discharge Coefficients of Square Edged Orifices for Measuring the Flow of Air, by H. 6. Bean, E. Buck ingham and P. S. Murphy (Bureau of Standards Journal of Research, Vol. 2, 1929, p. 561). 74 Flow Measurement by Nozzles and Orifice Plates (A.S.MJ5. Power Test Codes, Chapter 4 of Part 5 1940). " Air Flow Measurement in tbe Laboratory, by D. D. Wile (Refrigerating Engineering, June, 1947, p. 516). ** A.S.H.V.E. Research Report No. 1204--Entrainment and Jet-Pump Action of Air Streams, by G. L. Tuve, G. B. Priester and D. K. Wright, Jr. (A.S.H.V.E. Transactions, Vol. 48, 1942, p. 241). c A.S.H.V.E. Research Repohts Nos. 857, 911 and 966--Measurement of the Flow of Air Through Reg isters and Grilles, by L. E. Davies (A.S.H.V.E. Transactions, Vol. 36,1930, p. 201, Vol. 37, 1931, p. 619, and Vol. 39,1933, p. 373). ** A.S.H.V.E. Research Report No. 1162--Air Flow Measurements at Intake and Discharge Openings and Grilles, by G. L. Tuve and D. K. Wright, Jr. (A.S.H.V.E. Transactions, Vol. 46, 1940, p. 313). ** -S.H.V.E. Research Report No. 1092--The Flow of Air Through Exhaust Grilles, by A. M. Greene, Jr. and M. H. Dean (A.S.H.V.E. Transactions, Vol. 44, 1938, p. 387). "A.S.H.V.E. Research Report No. 936--Investigation of Air Outlets in Class Room Ventilation, by Larson' D- w- Nelson and R. W. Kubasta (A.S.H.V.E. Transactions, Vol. 38, 1932, p. 463). , -S.H.V.E. Research Report No. 1076--Air Distribution From Side Wall Outlets, by D. W. Nelson ttn M J' St?wart (A-S.H.V.E. Transactions, Vol. 44. 1938. p. 77). * A ^SUI^ng ^ Flw. by G. L. Tuve (Heating, Piping and Air Conditioning, December, 1941). * ,tHVE- ,esearch Report No. 1140--The Use of Air Velocity Meters, by G. L. Tuve, D. K. Wright, rr L` J` Siegel <A S H V-E. Transactions, Vol. 45, 1939, p. 645). (A 9 weTMperature Humidity and Air Motion Effects in Ventilation, by O. W. Armspach and Margaret Ingels ' w A q ` TransactioN0. Vol. 28,122. P- 103). k .. H-V.E. Research Report No. 1165--Development of Instruments for the Study of Air Distri- 1940p ^ ^ ^ra^' E* Hershey and R. B. Engdahl (A.S.H.V.E. Transactions, Vol. 46,