Microscale Organic Chemistry Glassware

Ground-glass joints. These are used to attach one piece of glass equipment to another with an air-tight seal. The outer, or female joint is conical with a slight taper, and "ground" or rough on the inside. It slides over the inner, or male joint which is conical with the same taper and ground on the outside. Together they make a tight seal and join the two pieces. The joints are expensive because they are made to precise sizes and must fit perfectly. They come in standard sizes, called "standard taper", and are identified by two numbers, the first indicating the diameter of the joint and the second indicating the length of the tapered part. The first number is most important in matching the inner and outer joints. There are three sizes of standard taper (Ts) joints in your microscale kit: 14/10, 7/10, and 5/5. Usually these numbers are written on the glass part near the joint to facilitate matching of joint sizes.

Conical Vials. These take the place of large, round-bottom flasks used in the traditional laboratory. Chemical reactions usually are carried out in these vials, and they can also be used for measuring and storing chemicals. Each one has an outer ground-glass joint and a threaded outer surface to allow attachment of other glassware. There are four sizes: 5.0 mL, 3.0 mL, 1.0 mL, and 0.3 mL capacity. The two large sizes have a 14/10 outer joint, the 1-mL vial has a 7/10 joint, and the smallest vial has a 5/5 ground-glass joint at the top.

Air Condensers. These are glass tubes with an inner joint at the bottom and an outer joint at the top. They are usually attached to a reaction vial (conical vial) and used to prevent vapors from escaping from a hot or boiling reaction. The vapors contact the cool, inside surface of the tube and condense into the liquid phase, dripping down the inside of the tube and returning to the reaction mixture. Air passing by the outer glass surface keeps the tube cool. The air condenser can also function as a simple mechanical extension to hold a conical vial in place in a cooling or heating bath. There are two sizes which differ in the size of the ground-glass joints: the larger one has a 14/10 inner joint on the bottom and a smaller, 7/10 outer joint on top; the smaller one has 7/10 joints on top and bottom. The joint size must be matched with the joint size on the conical vial you are attaching it to.

Water-cooled or Jacketed Condensers. These serve the same purpose as the air condensers, except that cooling is made more efficient by circulating cold tap water through an outer glass jacket. Water goes into the bottom connector and out the top to prevent trapping air in the water jacket. For lower-boiling liquids, this additional cooling is necessary to prevent the escape of vapors.

Claisen Head or Claisen Adaptor. This rather exotic piece of equipment places an offset in the plumbing of an apparatus with an access hole. This allows introducing chemical reagents (usually liquids) into a reaction mixture without taking apart the whole apparatus. If a teflon liner and screw-cap are secured on the access hole, liquids can be introduced with a syringe without exposing the reaction mixture to the atmosphere. With a screw-cap and "O" ring, a thermometer can be introduced through the access hole.

Hickman Distilling Head. This ingenious device replaces the traditional still, which is much larger and requires connecting and supporting a number of pieces of glassware. The purpose of a still is to heat a liquid until is passes into the gas (vapor) phase, and then allow the vapor to cool and condense back into the liquid phase, with the condensed liquid trapped in a second container. The Hickman still functions like the air condenser in condensing vapors with the cool glass surface, but the liquid drips down the inside to be trapped in a small circular depression, or collar, in the lower part of the tube. The bottom joint is a 14/10 inner joint and the top joint is a 14/20 outer joint.

Drying Tube. The drying tube attaches to the top of an apparatus with a 7/10 inner joint. The tube is used to protect the reaction from moisture in the atmosphere while still allowing the passage of air to equalize pressure. To accomplish this the tube is packed with a glass wool plug, a quantity of moisture-absorbing solid (the "drying agent"), and another glass wool plug. It is important to remove the drying agent and clean the tube after each use, since drying agents can harden and swell with time and become impossible to remove.

Craig Tube. The Craig tube is used for small-scale recrystallization, which is a method for the purification of small quantities of solid compounds. It has two parts: an outer body, which functions like a vial or test tube; and an inner plunger, which fits partly into the body and rests on a ground-glass surface. The ground-glass joint is not greased, so that liquids can leak through it but solids cannot pass.

Capillary Gas Delivery Tube. This long tube has an inner 7/10 ground-glass joint on one end, four 90^o bends, and a very small inside diameter. It is placed on top of a reaction apparatus in which gas is generated, and the gas passes through the tube to be collected in an inverted tube at the other end. Gas collection is used to measure the quantity of gas produced in a reaction, or to prevent toxic gases from escaping to the atmosphere.

Syringe. The syringe is really a medical device, but chemists use it regularly to measure and transfer small volumes of liquids. It consists of three parts: the body, which is calibrated according to volume and has a metal fitting, called a Luer-lock fitting; the plunger, which fits snugly into the body so that liquid cannot escape between the ground-glass outer surface of the plunger and the ground-glass inner surface of the body; and the needle, which is a hollow, pointed piece of stainless steel that connets to the syringe by way of the metal Luer-lock fitting.

Magnetic Stir Vanes. No, they do not operate by magic. The stir vane is made of teflon with a small magnet embedded in the center. The magnet tends to align itself with a large magnet mounted just under the surface of the heater-stirrer. When the stirrer motor is started, the large magnet rotates and the spin vane, trying to stay aligned, rotates at the same time. In this way a heterogeneous reaction mixture can be continuously stirred without having to open the reaction apparatus and introduce a mechanical stirring device. Homogeneous solutions do not usually require stirring, but chemists like to see something happening so they often use spin vanes to liven things up. The spin vane has a triangular shape that matches the triangular cross-section of the conical vials. It will not function unless it is placed in the vial with the point facing downward; it is a good idea to put it into the vial before adding chemicals or solvents. There are two sizes of spin vanes: the large one fits the two largest conical vials and the small one fits the 1-mL conical vial. They will not function in the wrong size vial, or in a beaker, vial, or flask which has a flat bottom. Spin vanes are very expensive and very easy to lose. You should clean them after each use and return them to the small vial that holds them.

Magnetic Stir Bars. These function on the same principle as the spin vane, but is designed for vessels that have a flat bottom. They will not function in a conical vial. They are just as expensive and easy to lose as the spin vanes.

Micro-spatula. This is one of the most useful devices in your microscale kit. The flat, long blade can be used to weigh out solids, stir mixtures, remove "O" rings, scratch glass surfaces to induce crystallization, and generally poke at solutions to see what's going on. Keep it clean so that reactions and chemicals are not cross-contaminated.