An IMPROVED CHEMICAL HOOD EUGENE C. BINGHAM Lafayette College, Easton, Pennsylvania
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HEMISTS are not expected to work under a hood except when their work makes the use of a hood necessary. This fact seems to prove that the problem of the chemical hood is still far from solved. It will be solved when chemists find it as agreeable to work under a hood as elsewhere. It is thus necessary to provide duplicate working space for each chemist, which greatly adds to the cost of laboratories. I n order to save expense the number of hoods is reduced, but the discomfort of those working a t the hoods is thereby increased. A study of the problem suggests several reasonsfor the chemist'sdislikeforthehood. The spacemaybecramped, the draught defective, the lighting may be poor, the windows may stick, the hood may be distant from one's other work, there may be lack of privacy for one's work, and there may even exist a lack of tidiness where several share the same working space. None of these reasons serves to explain the curse of the chemical hood, for all of these objections can he overcome, and yet the curse upon the chemical hood still remains. The real objection is connected with the posts between the various windows. They are often quite wide to contain the boxes in which run up and down the counterweights for the windows. If one considers that a chemist cannot be expected to be in physical contact with the posts, a considerable fraction of the working space is given over to the posts. On further consideration, one will observe that no useful purpose is achieved by having the counterweights occupy the most valuable space a t the front of the hood. They could equally well be carried to the rear of the hood or to any convenient point.
However, no matter how much the posts arereduced, so long as the posts remain the objection to the hood will remain. The reason for this is clear, for no one
FIGURE1.-A
PERSPECTIVE VIEW OI.
HOOD
works in front of a post, regardless of its size. If a chemist requires a certain space before a hood s, and the width of the window is w, the number who can work
at a given window is s/w, but only integral values count. Thus the fractions are all to be disregarded. Going from mathematics to ordinary language, by his arrangement of the posts the designer of the laboratory determines how many may work a t the hoods without crowding. The designer may not have bad any adequate
conception of the nature of the problem, and thus a very large part of the available hood space is rendered unavailable. Thequestion then arises as to whether it is not possible to do away with the posts altogether. As a matter of fact, hoods can be supported from the walls or ceiling. A false back of transite board can be used to afford space for the movement of noxious gases to the flue and also for the rise and fall of counterweights. Since the fumes are a t most very dilute, no trouble need be encountered from the rusting of metal. One difficulty in doing away with the posts is that the windows when pulled down would run out of their
guides and be subject to objectionable lateral motion. This difficulty is, however, easily and completely overcome in the following manner. An experimental hood was built to try out theidea, but not necessarily of the construction or material most
suited for later use, shown in perspective in Figure 1, and in front view in Figure 2. The posts (16) are cut off a t a convenient height, some six feet or more above the floor. The windows (14) are retained because they are needed a t times to prevent cross-currents when very noxious gases are in use, but the sashes (15) are extended upward above the
normal height of the windows, so that the windows can be pulled down all of the way without the sashes losing effective contact with the guides. In order that the windows may fit each other snugly even below the post i t is necessary to place the posts in a plane somewhat behind the plane of the windows. A simple tongue-andgroove construction is employed, shown in Figure 3 for
a section on the line 3-3 of Figure 2. The wood of the ings. The space is kept as free as possible to keep the tongues and of the posts was maple, and the surfaces ventilation unimpeded. Small blocks only are used to were smoothed and fitted carefully. The grooves attach the transite board to the wall. The counterwei~htsare conveniently placed in this space as shown in Figure 5, or springs may be used as indicated in Figures 1 and 2. This system does not require the strong fansnecessary for individual hoods, because when noxious gases are once in the space behind the "false" partition they need not move rapidly, since there is little resistance, no sharp bends, and no possibility of cross currents. Electric lights placed high within the hoods have been found very helpful, but they are not indicated in the figures. If i t becomes possible to work agreeably under hoods the question arises, "Why not save the duplication of space, combining desks and hoods?" This we have done with entire success a t the walls. The next question is, "Why not do away entirely with the wall hoods and use the desks in the middle of the laboratory, covered with the type of hood here illustrated?" We suggest that in this case a "false" ceiling must be used in place were greased originally, hut they have n i t required a of the "false" wall. second treatment in two years. Efforts are now being made to interest manufacturers The construction permits the ends of the hood to who will supply this type of hood in wood or metal to be raised and lowered, as well as the front, as shown those desiring it. It need not cost more than the forms of in Figure 6. hoods now in use. In use i t has heenfoundthoroughly In the end views, Figures 4 and 5, the space behind satisfactory in both an industrial and a college laborathe hood is well shown, with the upper and lower open- tory.
