In the book The Manipulation of Air-Sensitive Compounds by D.F. Shriver and M.A. Drezdzon, they give a inert atmosphere setup (figure attached) where inert gas flows from one inlet through the reaction flask to a mineral oil bubbler. However, during reaction and cooling they say to turn off the flow from that first inlet and turn on a second inlet flow of inert gas. I'm confused why there needs to be two inert gas inlets. Why can't there just be one inlet that is on the whole time for initial purging, reaction, and cooling? Shriver and Drezdzon mention that this two-inlet configuration prevents atmospheric gases from backing up into the system and minimizes exposure of the reaction mixture to impurities in the inert gas, but it seems to me that having one inlet would perform just as well.
Many thanks for your help.
I shall suppose that the flask is heated to boiling temperature during the essay. On cooling, vapour tends to condensate to increased extent both in the flask and at the condenser, with a resulting tendency to induce a certain level of vacuum, rather than the positive relative pressure expected during the experiment. This is avoided, and most effectively on the condenser side of the assemblage, by opening the second inlet flow line of inert gas. Otherwise the mineral oil bubbler could (possibly) inject oil back to the admission glass tube, and after that, air; while extra care would be needed to avoid air leakage into the flask, and to finally open the flask to recover its content at the end of the essay. Also prevented is the apparent possibility of the reaction mixture to enter into the condenser, what might possibly occur for negative relative pressure in the condenser side if the flask gets full of liquid and the first inlet gas line was not closed.
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