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WEIGHT OF ROUND, GALVANIZED-IRON PIPE, IN POUNDS PER RUNNING FOOT.
Gauge of Iron.
No. 28. No. 26. No. 24. No. 22. No. 20. No. 18. No. 16.
The temperature-controlling systems commonly employed with blower systems are automatic in operation. With such a system of control, it is simply necessary for the engineer to supply the heating system with sufficient steam. The thermostats regulate the temperature within 20 above or below that for which they are set.
The controlling apparatus usually installed consists of thermostats located in the rooms and connected by small air pipes to the valves or radiators and heaters, or to mixing dampers. The thermostats, operated by differences in temperature, alternately admit compressed air to and release it from the pipes. An air pressure of about 15 lb. is automatically maintained on the system by a pump or air compressor.
The air pressure at hand should also be used to operate remote dampers in heating ducts and vent flues, the actuation of the damper being effected by turning a valve on a switchboard conveniently located in the basement.
One of the best methods of arranging the temperature control of a building equipped with a blower ventilating system, in connection with which the heating is largely done by direct radiation, is to use diaphragm radiator valves that automatically shut off the steam from the radiators when the temperature of the room rises to 70°, or to whatever point the thermostat may be set.
The temperature of the air supply is kept at or near 70° by cold-air and warm-air thermostats. The one placed in the
cold-air room or duct is connected with the steam valves on a portion of the main heater, so that when the outdoor temperature rises above a certain point, and steam is no longer needed, it is automatically shut off.
The warm-air thermostat placed in the duct beyond the fan shuts off the balance of the heater when no longer needed. This thermostat alternately closes and opens the steam valves.
By-pass dampers are also used to by-pass cold air when the regulation of the temperature must be very close.
Supplementary heaters at the base of flues, when used in place of direct radiators in the rooms, are connected with the room thermostats, which permit the tempered air from the blower to flow through the supplementary heaters without being reheated when the rooms do not require heat; or, the supplementary heaters may be supplied with mixing dampers.
With a single duct system, the thermostats are made to operate the register blades or the damper in the pipes, controlling the temperature by cutting down the air supply.
DRYING AND COOLING AIR.
To make assembly rooms comfortable in hot weather the air forced into the rooms by the fan must not only be cooled, but its humidity must be kept within reasonable limits. In order to give the air an agreeable feeling of freshness, its humidity must be reduced to 40 per cent., or less. The regulation of the humidity of the cooled air may be accomplished in several ways.
1. The air may be cooled to a temperature considerably below that at which it is desired to admit it to the rooms, the moisture in the air being condensed and the air then warmed slightly to reduce the relative humidity.
2. A portion of the air may be heated as in (1), then be mixed with untreated air by-passed around the refrigerating coils or ice box; the proportion of the two being regulated to effect the desired result.
3. The air after being cooled may be passed over shallow trays containing calcium chloride, which is capable of absorbing about three times its own weight of moisture.
GAS AND GAS-FITTING.
KINDS OF GAS.
Coal gas is made by heating bituminous coal in air-tight boxes or retorts. The heat breaks up the combinations of hydrogen and carbon in the coal, transforming them into other compounds, most of which are gaseous at ordinary temperatures. Among the new compounds thus made are tar, ammonia, and sulphureted hydrogen. The tar and ammonia are condensed and removed. The gas also undergoes purification and scrubbing; in the former process, the gas is forced in thin streams through pans filled with lime, oxide of iron, etc.; and in the latter, through bodies of liquid charged with certain chemicals.
Oil gas is made from petroleum in a similar way and from almost any kind of oil, grease, or fat.
Producer gas differs from the coal gas commonly used for lighting, in having much less combustible matter, and in having a large percentage of nitrogen. It is made by burning anthracite or bituminous coal in a closed furnace, with a supply of air too small for complete combustion. The average quality of producer gas contains from 10 to 15 per cent. of hydrogen, from 20 to 30 per cent. of carbon monoxide (CO), and from 40 to 60 per cent. of nitrogen. Producer gas burns with a dull reddish flame, and its heating value is about onefourth that of good coal gas.
Water gas is made from anthracite coal and steam. The coal is placed in an air-tight cylinder, ignited, and raised to an incandescent heat by an air blast; the blast is then shut off, and dry steam is blown through the glowing fuel. The intense heat breaks up the steam into free oxygen and hydrogen, the oxygen combining with the hot carbon, forming CO, and the hydrogen passing along with it, but not combining. These are then led to a gas holder. The operations of blowing up and making gas alternate at intervals of about
3 minutes, until the fuel is exhausted. The fresh gas burns perfectly in heating burners, but when used for lighting purposes, is always enriched in carbon, by the vaporization of petroleum before it leaves the generator. The density of pure water gas is .4 that of air. It naturally has very little odor, but some impurities are allowed to remain to give the gas a perceptible odor.
Acetylene (chemical symbol, CH2) is composed of 12 parts of carbon to 1 of hydrogen by weight, or 92.3 per cent. carbon and 7.7 per cent. hydrogen. It is the most brilliant illuminating gas known. Its density is about .91, and its weight at 320 F. is .073 lb. per cu. ft. It is without color, and has a strong odor, like garlic. It is poisonous to breathe, in about the same degree as ordinary gas. The heat developed by the combustion of 1 cu. ft. is theoretically 1,385 heat units. Acetylene is manufactured by mixing calcium carbide with water. The carbide is a mixture of coke and lime which had been fused in an electric furnace. It is reddish brown, or gray, in color, somewhat crystalline, and decomposes water like ordinary quicklime; the calcium takes oxygen from the water, forming oxide of calcium, or common quicklime, while the carbon combines with the hydrogen of the water, and forms the desired compound, acetylene. Considerable heat is given off during the operation.
Pure carbide of calcium will yield 5.4 cu. ft. of acetylene per pound; but it is hardly safe to reckon upon more than 4.5 cu. ft. from the commercial carbide. Special burners are required for acetylene illumination, provided with small air holes to supply more air to the flame than is obtained by ordinary burners. Acetylene will give a light of about 240 candlepower when burned at the rate of 5 cu. ft. per hour, while good coal gas only gives 16 candlepower at the same rate of combustion. Acetylene can be reduced to liquid form, at a temperature of 60°, by a pressure of about 600 lb. per sq. in., but is then unsuitable for use in buildings, owing to the danger of explosion. Acetylene corrodes silver and copper, forming explosive compounds, but does not affect brass, iron, lead, tín, or zinc. These facts should be borne in mind when constructing apparatus for its use.