A vent is formed in the flask in such manner as to prevent accidental spillage of liquid therefrom while also permitting entrance of {HEAD ~ air} into {TAIL ~ the flask} when negative internal pressure is applied during removal of liquid therefrom 
into
A vent is formed in the flask in such manner as to prevent accidental spillage of liquid therefrom while also permitting entrance of { HEAD ~ air } into { TAIL ~ the flask } when negative internal pressure is applied during removal of liquid therefrom
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH