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HEATING VENTILATING AIR CONDITIONING GUIDE 1943 consists of a measuring burette, a leveling bottle, and three pipettes. Carbon dioxide is absorbed in the first pipette by potassium hydroxide, oxygen in the second by potassium pyrogallate, and carbon monoxide in the third by cuprous chloride. A known volume of gas is drawn in, and. after each of the three absorptions the reduced volume is again measured in the burette. Pressure and temperature of the gas sample are kept constant while measuring. Several passes are made through each pipette which contains tubes or glass beads to increase the wetted surface. It is essential that each reaction be completed before the next reaction is started. Since the life of the reagents is limited, it is well to keep a record of the number of samples tested. Cai;e is needed in operation to prevent the pulling of reagents out of the pipettes into the capillary tubing and burette. Many recording gas analyzers are available and are usually found in the larger plants. SMOKE DENSITY MEASUREMENTS A common method of determining the relative density of smoke issuing from chimneys is by visual comparison with the Ringelmann Smoke Charts. A sheet.of four ruled charts with varying weights of black lines is used. The sheet is 12 by 26 in.-overall on which are four charts, each consisting of 294 squares, 14 wide and 21 high. The width of line and spacings are given in Table 1. Table 1. Ringelmann Smoke Chart Spacings Number of Card i 2. 3 4 Thickness of LINES, MM 1.0 2.3 3.7 5.5 Distance in Clear Between Lines, mm 9.0 7.7 6.3 4.5 The charts are placed 50 ft from the observer and in line with the stack to be observed. At this distance the lines disappear and the charts appear as varying shades of gray. At times a white chart is added as No. 0 to the' left of the four charts 1 to 4, and a black chart to the right as No. 5. Apparatus using the photo-electric cell has been devised for recording smoke densities in large plants. CARBON MONOXIDE MEASUREMENT In garages and vehicular tunnels carbon monoxide is. a constant potential danger. In small amounts it causes headaches and inefficiency, and in larger concentrations it causes collapse and death in rather short periods of exposure. A method pf analyzing for carbon monoxide con centrations completes the oxidation of the carbon monoxide in a known volume of sample, in the presence of a catalyst. The heat resulting is measured by a thermocouple calibrated in parts per 10,000 of carbon monoxide34. *A Carbon Monoxide Recorder, by S. H. Katz, D. A. Reynolds, H. W. Frevert and J. J. Bloomfield (U. S. Bureau of Mines, Technical Paper No. 355,1926). 680 Chapter 36 MOTORS AND MOTOR CONTROLS Direct Current Motors, Alterating Current Motors for Single Phase and Polyphase, Special Applications, Classification of Motors, Manual Control, Automatic Control, Pilot Controls, Direct Current Motor Control, Squirrel-Cage Motor Control, Multispeed Motor Control, Wound Rotor Motor Control, Single Phase Motor Control THE electric motor, available in many different types suitable for various services, is now the most widely used form of prime mover. The equipment for starting, controlling and protecting these motors varies with the type and_with the functions it is desired to attain. Motors used for heating, ventilating and air conditioning applications may be divided into two general classifications: (1) for use with direct current, and (2) for use with alternating current. All driven machinery has certain torque characteristics which may vary with the speed, such as fans, which have sharply increasing torques with increasing speed. Others, such as reciprocating compressors, have a con stant torque characteristic with changing speed, while still others such as stokers, may have rising torque with decreasing speed. Motors with suitable torque characteristics should be applied to the-driven load. All electric motors, as with nearly all machines, are rated on the basis of the total temperature which the motor attains under operating con ditions as well as other characteristics. The motor temperature is a result of both the ambient temperature and temperature rise of the motor. The motortemperature rise is in turn determined by motor construction and motor losses. In selecting motors careful attention should be given to the ambient temperature, and rated motor rise in order that the resulting motor temperature does'not exceed allowable total temperature, otherwise greatly shortened motor life will- result. Consult motor manu facturers for allowable temperatures. DIRECT CURRENT MOTORS The three types of direct current motors 'available are: (1) shunt wound, (2) compound wound, and (3) series wound. Shunt Wound motors, being suitable for application to fans, centrifugal pumps, or similar equipment, where the amount of starting torque required is relatively small, are used for the majority of applications in the field of heating, ventilating and air conditioning. They may be used on recipro cating pumps and compressors, if started under unloaded conditions. 681