AN IMPROVED APPARATUS FOR DEMONSTRATIONS WITH GASES WELKER BECRTEL R w n e H i g h School and Junior College, B w n e , Iowa
FOR schools with an inadequately ventilated lecture table and not enough hoods to enable a class to experiment with poisonous gases safely in the laboratory, the following apparatus will be of value. I t can be used to show the preparation and properties of chlorine, hydrogen sulfide, sulfur dioxide, ammonia, oxides of nitrogen, and hydrochloric acid.
potassium permanganate in the generating bottle and fill the dropping funnel with concentrated hydrochloric acid. Permanganate is superior to manganese dioxide because no heat is required, and the reaction practically stops as soon as the flow of acid is cut off. The lower train consists of two bottles which contain 10 g. of sodium sulfite in 50 ml. of water. Hypo may be used instead, but a precipitate of sulfur forms. The bottles in the upper train are for the demonstration. The first contains water to remove hydrochloric acid carried over from the generator. The second contains concentrated sulfuric acid to dry the gas somewhat. In the demonstration of bleaching, the third contains dry colored cloth, litmus paper, and paper with spots of writing ink and India ink. In the next bottle are these same materials, moistened. The last bottle contains a solution of sulfite to absorb excess chlorine. For the demonstration open the stopcock of the dropping funnel to allow the acid to drip slowly. Chlorine forms a t once and is sent into the upper train. As soon as bleaching is shown, direct the gas into the lower train while the bottles used for bleaching are removed The illustration shows a gas generating bottle fitted as a unit and taken to the hood. To show the action with a three-holed rubber stopper. A dropping funnel of chlorine with metals, non-metals, and compounds of is used, and a glass tube connects the neck of the drop- hydrogen, insert three bottles in place of those removed. ping funnel with the generating bottle to equalize the The first of these contains a sheet of thin copper foil. pressure. In this way back pressure, which may cause The second has an extra hole in the stopper; in this is a acid to splash out if it becomes sufficient to send bubbles medicine dropper. The medicine dropper is filled with of gas up the stem of the dropping funnel, is prevented. powdered arsenic or antimony, and the opening is The third hole in the stopper carries the delivery tube closed by a thin layer of vaseline. In the third is a tuft which leads to a three-way glass stopcock. This en- of absorbent cotton moistened with turpentine. Pass ables the operator to send the gas through either of two chlorine through these bottles. The copper reacts with trains of bottles. The bottles in the lower-train should a bright flash. As soon a s the next bottle is filled with contain a solution of an appropriate absorbing agent gas, press the bulb of the medicine dropper quickly. while those on the top contain the chemicals which are As the powder sprays out it catches fie. When the gas to form a part of the demonstration. This device comes in contact with the turpentine i t forms white enables one to fill the demonstration bottles one a t a fumes of hydrochloric acid and the cotton soon becomes time and then send the excess gas into the lower train so black. By directing the gas into the lower train after that each reaction can be observed and studied before each reaction the experiments can be performed sepathe next begins. If it is necessary to remove bottles rately, so that there is ample time to study each before from the upper train it can be done without any ap- the next is begun. The common experiments usually performed with the preciable amount of gas escaping. A detailed description of the use of the apparatus for other gases named in this article can be adapted easily the demonstration of chlorine follows. Put 25-30 g. of for use with this apparatus.