Apparatus for Inert Gas Systems AMOS TURK Boone-Turk Oil Development Laboratory, Pittsburgh, Pennsylvania
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T IS frequently necessary to carry out operations In an atmosphere of an inert or other gas. The method used to accomplish this usually consists of sweeping the inert gas through the system until any foreign gas present is completely displaced. The disadvantages of such a procedure are the long and uncertain length of time needed to complete the gas flushing, the waste of gas, and the danger of incomplete displacement in inaccessible portions of the system. A more certain procedure involves three or four evacuations of the system, and refilling with the inert gas after each evacuation. In order to carry out such an operation, an extremely simple apparatus has been designed which eliminates the use of mercury manometers, numerous stopcocks, and other costly or bulky equipment. All that is needed is a small "lecture table" tank of the inert gas (e. g., nitrogen), a T-stopcock, and a test tube coutaining some mercury. When the displacement of foreign gas (e. g., air) by nitrogen is complete the apparatus is ready, without further change, for maintaining the nitrogen atmosphere for any length of time with a minimum waste of the gas. PROCEDURE
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With the stopcock in the position (see diagram), the entire system is evacuated by a water aspirator or any other convenient vacuum source. Rubber tubing a is thin walled and therefore collapses, whereas thickwalled rubber tubing b does not. The stopcock is then
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turned to the position (without removing the source of vacuum) and the valve of the tank is carefullv opened untk rubber tubing a has regained its normal shape. The valve is then immediately closed. Using the small "lecture table" type of tank i t is very easy, with a little practice, to reach a pressure close to or a little above one atmosphere in this way. A large tank equipped with a reducing valve is also suitable. If too much pressure is applied by accident, the only harmful result will be that one end of tube a will be forced off. T
The stopcock is now turned back to I and the system is thereby re-evacuated. This operation may be repeated three times to insure a complete nitrogen at-
mosphere. After the system has been filled with nitro-
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gen for the last time and the stopcock is in the position, the source of vacuum is removed and test tube d containing mercury is placed around the lower leg, c, of the stopcock, as shown by the dotted lines, so that c dips into the mercury to the depth of one or two centimeters. The test tube may advantageously be supplied with a one-hole, grooved cork to prevent splashing out of mercury. The stopcock is then turned slowly counterclockwise toward position --I. If the pressure in the system is less than atmospheric, mercury will start to rise in c. The stopcock is then turned back a t
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once (clockwise) to and a little more gas is introduced into the system. Wben the pressure is one atmosphere or more, and the stopcock is turned counterclockwise toward the +position, the mercury in the test tube will be undisturbed or the excess gas pressure will be released by bubbling through the mercury. With the stopcock still in the --I position, a small amount of nitropen is released from the tank to remove the residual
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air in tube c. The stopcock is' then turned to and the apparatus has now assumed the form of the usual gas trap and is ready for use. The nitrogen atmosphere can be maintained in the system indefinitely by bubbling the gas slowly through the mercury gas trap, or by closing the tank completely and adding some nitrogen to the system only a t such times that a deficiency of pressure is indicated by a rise of mercury in c. - The apparatus described has been used with conGenience and time saving in this laboratory for many operations.
