A DEVICE FOR TRAPPING OFFENSIVE GASES A trap has been devised which prevents the escape of certain gases into the laboratory. The gases are forced to escape into a neutralizing gaseous atmosphere. The trap i s sz~ccessfulin a room without hoods or unusual wentilating facilities. The principle inwolwed i s general and has wide application. Among the problems confronting the teacher of laboratory courses in chemistry the prevention of the escape of offensive gases into the room is perhaps less amenable to treatment than others. Student carelessness of course leads in the list of reasons why such gases should escape but the experienced teacher will agree that From this is a fault which is always generator present and difficult to correct. Any scheme of prevention must take this into account if any degree of success is to be attained and the purpose of this paper is not to submit a foolproof device but to suggest a scheme and a general principle upon which other schemes can be devised which will reduce somewhat the need for extreme $ care on the part of the student and make feasible the preparation of substances under conditions which otherwise would deter the experienced instructor from even considering their preparation. The principle upon which the device to he described depends for its efficiency is the maintenance of a neutralizing atmosphere of gas around the outlet of the tube from which the surplus portions of the gaseous products are forced to make their escape. For acid gases or acid-forming gases such as hydrogen chloride, hydrogen sulfide, and chlorine this neutralizing atmosphere is most conveniently ammonia. The set-up described contains no pieces of apparatus not easily obtainable by the student. It requires no technic not usually required of students in beginning chemistry. Its effective use depends only on the student's understanding of the principles involved and his cooperation in their application. The bottle, A , in which the samples are collected is suspended from the rubber stopper by friction. If the collection bottles are too heavy they may be supported by other means but the ordinary eight-ounce gas bottle pre1475
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JOURNAL OF CHEMICAL EDUCATION
AUGUST,1932
sents no difficulty without other support. The stopper hangs from the two bent glass tubes supported by a ring on a stand or the top portion of the circumferenceof the stopper may he fixed in a clamp and leave room for the suspension of the bottle below. During the evolution and collection of gas the escape tube from A leads to the Erlenmeyer flask, B, in which is placed some ammonium carhonate wet with sodium hydroxide solution. The flexible joint, C, permits flask B to be removed easily. For the ordinary experiment which is assigned to students in general chemistry three or four grams of ammonium carhonate is sutticient. The solution of sodium hydroxide should be normal or stronger. This trap is surprisingly efficient in trapping the overflow of such gases as were mentioned above. Chlorine from the generator of the most careless student who heats his generator too hot and fails to remove collection bottles when filled is effectively stopped. Not even the faintest odor of chlorine emerges from the trap. Since the other gases mentioned are less disagreeable and also easier to trap they need not enter into this discussion. When the bottle, A, is full, i t is removedandquickly replaced by another which is filled while the first is being observed and tested. This continues until the last bottle of gas for testing is collected. It is replaced by a bottle containing a small quantity of the wet ammonium carbonate. Each bottle of gas upon which the tests have been completed receives a small dose of the contents of the trap and the remainder of the ammonium carhonate is covered with more sodium hydroxide and the mixture poured cautiously into the generator until evolution of gas has stopped. The generator is then filled with water and emptied without gny danger of gas escaping. It is possible for a student using the above method to prepare and test repeated samples of chlorine and discharge his generator without liberating a noticeable trace of the gas in the room. This experiment can be safely performed in a room not equipped with hoods and without extra provision for ventilatidn. The principle involved in the trap, namely, that an escaping gas is more successfully trapped by a gaseous reaction than i t is by some heterogeneous reaction, such as bubbling through liquids, is perfectly general in its application and can he conveniently applied to gases and vapors other than those mentioned.
