D. K. Alpern Brooklyn College Brooklyn, New York
A Test Tube Automatic Gas Generator
A n automatic generator for producing common gases, comprising a test tube and available accessories, can easily be assembled by students for individual use. It is another modification of the Kipp (Banks, Schroeder, Starkey, etc.) generator, and was devised by the writer in 1936 to enable each person to have a simple, workable, and safe gas source. Jn the twenty-two years of use in freshman classes, there has been no explosion of hydrogen. The photograph, Figure l A , shows the generator in operation while 1R indicates the "stand-by" condition. As illustrated in the line drawing, Figure 2, one No. 4 two-hole rubber' stopper, holding a thistle tube and a gas effluent tube, tightly fits the mouth of a 25 X 200mm test tube. The top half of a second similar No. 4 stopper is cut off, and the stem of the thistle tube inserted in one of the holes of the bottom piece so that this smaller stopper just slides easily into the test tube. The second holes of each stopper should be in the cis position relative to the thistle stem in order that the assembly may fit. Pieces of the required solid reactant (e.g., Zn for HI) are placed around the thistle stem 011 the top of the smaller stopper, and the assembly lowered into the test tube. Care must be taken to avoid dropping any
zinc into the bottom of the test tube as that n-ould make the automatic cycle inoperative. A pinch-clamp on the rubber sectiou of the gas
Figure 2
Neoprene should be used when NO2is generated by the action of copper in nitric acid.
Figure
delivery tube controls gas flow in the usual way. With the pinch-clamp open, the liquid reactant is poured down the thistle tube until its level is just above the solid reactant. The resultant reaction should be allowed to proceed for two minutes or so, in order to drive out air, and then the clamp should be closed. Continuing evolution of gas will increase the pressure in the generating tube, forcing the liquid surface to be lowered to a level just below the solid, with the liquid simultaneously rising in the thistle tube which thus acts as a reservoir. Opening the pinch-clamp releases gas as wanted. With such a convenient and small gas generator, semimicro process experiments become feasible. Thus, 0.5 g of copper filings in the center of a Pyrex tube (about 12 inch X bore) can be oxidized and subsequently reduced, without transfer and with a readily achieved precision of +l%,with the accompanying synthesis of water clearly demonstrable.
