Round-bottom flask

Round-bottom flasks (also called round-bottomed flasks or RB flasks) are types of <a href="/facts/Laboratory_flask/9puakCDX">flasks</a> having spherical bottoms used as <a href="/facts/Laboratory_glassware/M4CMuHRh">laboratory glassware</a>, mostly for <a href="/facts/Chemistry/SrNqkGVm">chemical</a> or <a href="/facts/Biochemistry/fa2pWEBp">biochemical</a> work. They are typically made of <a href="/facts/Glass/hezRsAGf">glass</a> for chemical <a href="/facts/Chemically_inert/oglbxzgk">inertness</a>; and in modern days, they are usually made of heat-resistant <a href="/facts/Borosilicate/Ywaqt7Ic">borosilicate</a> glass. There is at least one tubular section known as the neck with an opening at the tip. Two- or three-necked flasks are common as well. Round bottom flasks come in many sizes, from 5 mL to 20 L, with the sizes usually inscribed on the glass. In pilot plants even larger flasks are encountered. 
The ends of the necks are usually conical <a href="/facts/Ground_glass_joint/FzmKPLXw">ground glass joints</a>. These are <a href="/facts/Standardized/vS9AhNMS">standardized</a>, and can accept any similarly-sized tapered (male) fittings. <a href="/facts/Ground_glass_joint/FzmKPLXw">24/40</a> is common for 250 mL or larger flasks, while smaller sizes such as 14/20 or 19/22 are used for smaller flasks.
Because of the round bottom, cork rings are needed to keep the round bottom flasks upright. When in use, round-bottom flasks are commonly held at the neck by clamps on a stand.
A round-bottom flask is featured prominently on the logo of the <a href="/facts/Organisation_for_the_Prohibition_of_Chemical_Weapons/JdE4bTa9">OPCW</a>, the implementing body for the <a href="/facts/Chemical_Weapons_Convention/eP3Vsv5o">Chemical Weapons Convention</a>.

Round-bottom flask open-in-new

Round-bottom flask