University of Illinois Urb@na,Illinois 61801 '
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The use of gases, whether as reactants or as inert atmospheres to exclude air, has become a common operation in the chemistry lahoratory. The most frequently used pressure control apparatus is a bubhler.' Unfortunately, an ordinary bubhler consumes large quantities of gas if it is run for a long time. We have found that the following solenoid controlled bubbler reduces the use of inert gases during the reflux and distillation of dried, oxygen-free solvents by a t least a factor of ten. For reactions involvinr! cases as reagents, the bubbler reduces the quantities of gaselused and also minimizes the potential hazards. The reactant gas can be supplied at atmospheric pressure when needed without the continuous release of toxic or corrosive vapors. The cumulative effects of small quantities of impuritieb in reaction gases are minimized hecause there is not a constant flow of gas into the reaction vessel.2 As shown in the schematic drawing, the bubbler consists of a float which drops to comp1t:te aciicuit when the prrssure of the system dropi. The sulenoid valw IS opened,admitting gas to raise the system pressure to the point that it causes the oil level to lift the float off the contact to stop the gas flow. Gas is vented into an ordinarv bubbler if the Dressure rises too high. Mineral oil works well in tht. huhhle;. 'I'he solenoid rontrolled buhhlcr can he constructrd with readily available mittrrinls and touls for under 32.5. The main rmrt ofthe huhbler a~nsistp,ofa 250-ml filter flask that i i fi1tt:d kith a 2 cm X 30-cm glass tube through a stopper. A second side arm is included on the flask for the wire from the bottom contact. Additional side-arms may be added as in the schematic, or several Y-tubes can be used to accommodate the rubber tubing. The wires into the flask may be glued in place, hut we preferred using a rubber septum cap as the seaL3The float is made from a cork stonner with a ball ~ o i nDen t s~rinr! in the hole through the cork sothat the sprinhfunctions th;! contact to the center wire. The spring is soldered to a washer, which is glued to the bottom of the cork to serve as the top electrical contact. The float rides on a wire strung between the caps on the bottom and top of the glass tube where the wire is screwed tightly with a wing nut. The caps on the glass tube I Shriver, D. F., "The Manipulation of Air Sensitive Compounds," McGraw-Hill,New York, 1969, p. 145. We have found that commercial carbon monoxide, for example, has traces of oxygen and carbon dioxide that become significant when large quantities of CO are bubbled through an air sensitive salution. "vailable from Aldrieh Chemical Company, 940 W. Saint Paul Ave., Milwaukee, Wisconsin 53233. The solenoid we use is a 120-V serial No. 100195, Catalog No. 8262C13 from the Automatic Switch Co., Florharn Park, New Jersey.
652 / Journal of Chemical Education
are round Plexiglas" or Teflon" with holes drilled through them to let oil pass through the bottom to lift the float. The bottom contact is another washer glued to a piece of Plexiglas@ and held in place on the center wire by a screw. The bottom contact has four nieces of CoDDer wire about l-cm long soldered on the bottbm washer i d b e the point of contact.Once the bottom contact is in dace, the minimum pressure that will activate the solenoid &he changed by raising or lowering the tube in the stopper. The wiring diagram shows that 120-V line voltage is used. An additional toggle switch is included to allow a bypass of the float circuit to open the solenoid for the initial purging of the reaction vessel with gas. The basic design of the bubble is quite flexible, and there is no reason why other nonconducting materials, such as Teflon", could not be used in place of Plexiglas" for the top and bottom. Many solenoids are available that fill the requirements for this bubbler.4 The brass fittings to connect the solenoid to a hose are available a t most hardware stores.
Figure 1. Schematicdrawing of the solenoid controlled bubbler
d Figure 2. Wiring schematic drawing far the solenoid controlled bubbler.
