AN EFFICIENT FUME HOOD GEO. W. MUHLEMAN Hamline University, Saint Paul, Minnesota
T
HE author has previously published in Indwtrial [I?, 316 (1925)l on chemical hoods. During the summer of. 1934 he was privileged to construct a fume hood which may be bluntly described as "fool-proof." The accompanying photograph gives a general idea as to the construction and appearance. and Engineering Chemistry
As is to be noted the hood is built on top of the laboratory table and is made up of eighteen individual hoods. There is a space of 12 inches between the top of the table and the bottom of the hood, i . e., room enough for gas and water pipes to be installed for Bnnsen burners and water pumps. Each individual hood is 22 inches long, 16 inches high, and 11 inches deep. There wasno especial reason for these particular lengths other than the necessity to supply each of the eighteen students, assigned to the laboratory table, a hood. The height admits a tripod upon which may be placed a 400-cc. beaker. At the top of each hood and as near
the center as possible is a hole 3 inches in diameter. This hole opens into a vent 11 by 3 inches which extends the entire length of the hood. On top of the hood in the very center is a 1 / 8 - ~ . ~ .motor which drives the exhaust fan. The fumes are driven to the outside of the building through a six-inch pipe. The interior was painted with asphalt paint. The criticism that wood construction constitutes a fire hazard may very properly be offered. But this hood was constructed as an experiment. At the end of a semester's use it may be reported that the hood has been found to be mechanically perfect and very efficient and warrants the construction of a similar hood of non-combustible material." Each individual compartment has a door hung from the top by spring hinges, which insures that all doors to the hood will be kept closed. Each door is fitted with a small window glass, 5 by 5 inches, so that the student may observe the progress of h k evaporation, precipitation, or digestion. A small hole in the bottom of the hood allows the passage of the rubber hose for the Bunsen burner to the gas cock on the outside. The fumes from the eighteen hoods, when in full operation, are efficiently carried to the outside by the fan. AS is obvious, the heated fumes from each of the eighteen hoods would naturally have a tendency to rise and perhaps produce some upward pressure so as to supplement the pull produced by the fan. In other systems of ventilation when the attempt is made to ventilate the entire laboratory an extra drain is made upon the heating plant, due to the amount of cold air that must be heated to take the place of the air blown from the room. With this type of hood almost enough heat is produced within the hood to develop sufficient hot air currents to force noxious fumes to the outside. This paper is submitted with the hope that the device described may be of interest to some teachers in schools and colleges whose ventilation problems demand a simple, cheap, but efficient hood.
