RUBBER BALLOONS for DISPENSING GASES CHAUNCEY C. HALE University of Wisconsin Extension Division, Milwaukee, Wisconsin
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S THE science of chemistry develops, it often seems desirable to incorporate new material into the beginning course in chemistry. Thus the beginner's load often exceeds that which the average student can carry advantageously. Likewise in the laboratory the instructor is inclined to emphasize quantity rather than quality and in the end accomplish less. It has been our aim to reduce the routine, time-consumine. overations to a minimum, and substitute material of a more valuable character, such as experiments involving quantitative manipulation for the chemistry major, and everyday practical material for the liberal education student. In order to procure material for experiments relating to gases preparations must precede the actual testing of the physical and chemical properties. Often as much or more time is spent in the collecting, assembling, and disassembling of apparatus as is required in the actual investigation of the properties. The dispensing of compressed gases to the student offers certain mechanical difficulties not encountered in dealing with solids or liquids. Providing the laboratory with a pipe line connected to a high-pressure gas cylinder through a reducing valve does not put the gas in the hands of the student. Furthermore, to limit the danger, an individual line is necessary for reactive gases. A
Equipment of the type shown in the illustration has proved satisfactory in use. The student is supplied with a gas balloon which he equips with a one-hole rubber stopper, glass tube, rubber connection, and screw cock. He then has a container which can be filled for him a t the supply room and from which he can remove the gas to be used as the work requires. No doubt every laboratory supenisor sighs with relief when his class has finished the work on hvdroe.en without a serious accident. With the balloonmet~od the rhanws of an explosion are remote, ior the gas is pure to start with; furthermore, if it docs explode, there will be no flying glass to injure the operator or those near him. Since the balloon merely replaces the gas generator, the student still has the experience of collecting gases over water or by upward or downward dhplacement of air. From his subject matter on the sources of the gas in question, he has learned the laboratory method of preparation. As many of our students have previously studied high-school chemistry, they have little to gain in repeating the use of the generator. Also, several gases, such as hydrogen chloride and chlorine, remain for which it will be necessary to set up a generator. Compressed gases can now be obtained a t reasonably close distributing centers, and when purchased in large cylinders, the price is moderate. Suitable reducing valves are available, and the manufacturers have taken necessary precautions so that the valves for certain gases may not be used on another tank from which the issuing gas will react with the original one. A reducing valve of the precision character is highly advised for hydrogen. Special gas balloons may be obtained from rubber manufacturing companies by the gross for a cost of a few cents apiece.
