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AUTOMATIC GAS GENERATOR IRVING FINE Morris High School, Bronx, New York
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BOUT five years ago, in an elementary course in qualitative analysis, the question arose as how to best generate the required H2S. Although a Kipp generator was tried for a time, its use soon had t o be discontinued. The apparatus proved to be too great a temptation to some of the more mischievous students, with the result that i t was frequently out of commission just when needed. Recourse was then had to individual test-tube generators, but these also had to be discarded, due to the unavoidably large supply of gas that was evolved. An extremely satisfactory solution to the problem was gradually worked out and is illustrated in Figures 1 and la. A piece of copper strip, ll/z inches wide and about 4 inches long, was bent into the form of a triangle and placed on edge in a standard wide-mouthed bottle. A circular piece of copper gauze, of the same diameter as the inside of the bottle, and with a '/%-inch hole in the center, was placed on the supporting copper strip. The ferrous sulfide was put upon the gauze, and the bottle was stoppered with a two-hole stopper carrying a delivery tube and a glass funnel. (After much experience with the unavoidable breakage that commonly results when thistle tubes are used, Mr. Gustav L. Fletcher, Chairman of the Physical Science Department, James Monroe High School, Bronx, New York, had for some time past been nsingfunnels instead. This practice certainly makes for greater economy and is to be strongly commended.) A screw clamp, attached to the delivery tube line, effectively controls the evolution of gas. When the clamp is closed, the excess acid collects in the funnel and the reaction stops. To charge the generator, the bottle is inclined and the ferrous sulfide is placed upon the gauze, care being taken that none drops below the gauze. After stoppering the bottle and standing i t upright, the clamp is opened and enough acid is added through the funnel to make contact with the ferrous sulfide. Mmor adjustments of the clamp can thsn be made to regulate the flow of gas. (If the funnels available are too short to reach to the bottom of the bottle, the stems should be lengthened by additional pieces of rubber or glass tubing.) It is advisable to stand the bottle in a ring on a ring stand; this will eliminate accidental tipping. As an additional safeguard against spilling of the acid, the funnel may be covered with a watch glass. This model can easily be adapted to the preparation of such gases as HZ,0 2 (oxoue method), COa, HCl, SOz (NazSOa method), GH2, Clz, CO, NO, and NOz. Upon Mr. Fletcher's suggestion, an attempt was
made to have the wire gauze anchored firmly in the bottle by means of a series of hollow glass studs, arranged horizontally, and molded in the bottle during manufacture. A bottle of this design was made, but a perforated Coors porcelain filter disc, with a %-inch hole in the center, was substituted for the copper gauze. Standardizing on such a single generator, capable of being distributed for individual pupil use for making any of the gases commonly 'iequired, obviously has many advantages. There is no longer any need for stocking such a large variety of flasks and bottles of different types and sizes; automatic control makes for greater economy in the use of reagents; the need for hoods is minimized; the work of the pupil, the teacher, and the laboratory assistant is greatly simplified. For quantity production of gases, a larger generator can be used in which the funnel is replaced by a tube leading to a supplementary storage bottle (Figure 5). A description of some of the other preliminary models developed, all of which have been tried out in the classroom, might be of interest. Figure 3 illustrates a design in which pebbles were used. Although this model was used to prepare each of the gases ordinarily required in a high-school course, it had one drawback. At times, small particles of the solid reagent used would drop down into the spaces between the pebbles, interfering greatly with the automatic control.
A cylindrical piece of rubber sponge also was tried (Figure 4), but this was found not to stand up as well as the other materials used. Until the porcelain model is available on the market, however, the copper model (Figures 1 and l a ) should
prove satisfactory for most purposes. It is simple enough to assemble to permit its distribution for individual pupil use. (Note: i t will be found best t o use large crystals of the solid reagent, rather than the reagent in powdered form.)
