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Ground glass joint
Ground glass joints are used in laboratories to quickly and easily fit leak-tight apparatus together from interchangeable commonly available parts. For example, a round bottom flask, Liebig condenser, and oil bubbler with ground glass joints may be rapidly fitted together to reflux a reaction mixture. This is a large improvement compared with older methods of custom-made glassware, which was time-consuming and expensive, or the use of less chemical resistant and heat resistant corks or rubber bungs and glass tubes as joints, which took time to prepare as well.
One of the glassware items to be joined would have an inner (or male) joint with the ground glass surface facing outward and the other would have an outer (or female) joint of a correspondingly fitting taper with the ground glass surface facing inward. To connect the hollow inner spaces of the glassware components, ground glass joints are hollow on the inside and open at the ends, except for stoppers.
Crude versions of conically tapered ground glass joints have been made for quite a while, particularly for stoppers for glass bottles and retorts. Crude glass joints could still be made to seal well by grinding the two parts of a joint against each other using an abrasive grit, but this led to variations between joints and they would not seal well if mated to a different joint.
During the 1920s efforts to standardise joints began, and some manufacturers started to produce joints that were standardised, but only within their own products lines. Commercial standards for joints began to appear around 1930 which allowed interchangeability of parts between different manufacturers. A notable proponent of this standardisation was Fritz Friedrichs. These days, ground glass joints can be precisely ground to a reproducible taper or shape, and joints of the same specification are reliably interchangeable.
Two general types of ground glass joints are fairly commonly used: joints which are slightly conically tapered and ball and socket joints (sometimes called spherical joints).
The conically tapered ground glass joints typically have a 1:10 taper and are often labeled with a symbol ST, consisting of a capital T overlaid on a capital S, meaning "standard taper". This symbol is followed by a number, a slash, and another number. The first number represents the outer diameter (OD) in millimeters at the widest point of the inner (male) joint. The second number represents the ground glass length of the joint in millimeters. Internationally the ISO sizes are used with 14/23, 19/26 and 24/29 very common in research laboratories, with 24/29 the most common. In the US the ASTM sizes (equal to the now obsolete Commercial Standard 21) are used with common sizes being 14/20, 19/22, 24/40 and somewhat 29/42. In the US 24/40 is most common.
For ball-and-socket joints (also known as spherical joints), the inner joint is a ball and the outer joint is a socket, both having holes leading to the interior of their respective tube ends, to which they are fused. The ball tip is a hemisphere with a ground-glass surface on the outside, which fits inside of the socket, where the ground glass surface is on the inside. This type of joint separates freely and must be held together with a clamp. Ball-and-socket joints are labeled with a size code consisting of a number, a slash, and another number. The first number represents the outer diameter in millimeters of the ball at its base or the inner diameter in millimeters at the tip of the socket, in both cases where the diameters are their maximum in the joints.
The second number represents the inner diameter of the hole in the middle of the ball or socket, which leads to the inner diameter of the tube fused to the joint.
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Ground glass joint
Ground glass joints are used in laboratories to quickly and easily fit leak-tight apparatus together from interchangeable commonly available parts. For example, a round bottom flask, Liebig condenser, and oil bubbler with ground glass joints may be rapidly fitted together to reflux a reaction mixture. This is a large improvement compared with older methods of custom-made glassware, which was time-consuming and expensive, or the use of less chemical resistant and heat resistant corks or rubber bungs and glass tubes as joints, which took time to prepare as well.
One of the glassware items to be joined would have an inner (or male) joint with the ground glass surface facing outward and the other would have an outer (or female) joint of a correspondingly fitting taper with the ground glass surface facing inward. To connect the hollow inner spaces of the glassware components, ground glass joints are hollow on the inside and open at the ends, except for stoppers.
Crude versions of conically tapered ground glass joints have been made for quite a while, particularly for stoppers for glass bottles and retorts. Crude glass joints could still be made to seal well by grinding the two parts of a joint against each other using an abrasive grit, but this led to variations between joints and they would not seal well if mated to a different joint.
During the 1920s efforts to standardise joints began, and some manufacturers started to produce joints that were standardised, but only within their own products lines. Commercial standards for joints began to appear around 1930 which allowed interchangeability of parts between different manufacturers. A notable proponent of this standardisation was Fritz Friedrichs. These days, ground glass joints can be precisely ground to a reproducible taper or shape, and joints of the same specification are reliably interchangeable.
Two general types of ground glass joints are fairly commonly used: joints which are slightly conically tapered and ball and socket joints (sometimes called spherical joints).
The conically tapered ground glass joints typically have a 1:10 taper and are often labeled with a symbol ST, consisting of a capital T overlaid on a capital S, meaning "standard taper". This symbol is followed by a number, a slash, and another number. The first number represents the outer diameter (OD) in millimeters at the widest point of the inner (male) joint. The second number represents the ground glass length of the joint in millimeters. Internationally the ISO sizes are used with 14/23, 19/26 and 24/29 very common in research laboratories, with 24/29 the most common. In the US the ASTM sizes (equal to the now obsolete Commercial Standard 21) are used with common sizes being 14/20, 19/22, 24/40 and somewhat 29/42. In the US 24/40 is most common.
For ball-and-socket joints (also known as spherical joints), the inner joint is a ball and the outer joint is a socket, both having holes leading to the interior of their respective tube ends, to which they are fused. The ball tip is a hemisphere with a ground-glass surface on the outside, which fits inside of the socket, where the ground glass surface is on the inside. This type of joint separates freely and must be held together with a clamp. Ball-and-socket joints are labeled with a size code consisting of a number, a slash, and another number. The first number represents the outer diameter in millimeters of the ball at its base or the inner diameter in millimeters at the tip of the socket, in both cases where the diameters are their maximum in the joints.
The second number represents the inner diameter of the hole in the middle of the ball or socket, which leads to the inner diameter of the tube fused to the joint.