Below is a modern Vacuum Atmospheres glovebox and below that is an older and lower-tech (lower cost) example:
Gloveboxes are sometimes equipped with electronic sensors to monitor oxygen and water content. In addition, a variety of (cheaper) chemical means are also used. For example, dialkyl zinc reagents react vigorously with water to make dense fumes of ZnO even at very low oxygen or water concentrations. If you open your diethyl zinc bottle and it fumes, your atmosphere is less than perfect (Note: if you did this outside the box, you would have a bright blue flame!).
Older and cheaper varieties of gloveboxes do not come equipped with fancy recirculators etc., but can still be useful. The easiest way to purify an atmosphere in such a box is to open a purge valve on the box (vented to a fume hood) and purge the box with a high purity inert gas. It is necessary to purge the box on a daily basis as oxygen can diffuse directly through the gloves even under positive pressure, especially if there any leaks or pinholes.
|A glovebox is not much good if you don't have a way of getting your materials in and out. If you look at the pictures above, you'll notice that there is a sealed chamber on the right side of the glovebox. This chamber is called the antechamber (or "port" by some) and it has two doors -- one that can be opened only from the inside of the box and one that can be opened only from the outside. As you can see in the photo on the left, the outer door to the antechamber is open, ready for glassware to be placed inside. See below to see how the antechamber is used.|
The antechamber can be evacuated with a pump or filled with nitrogen gas. Never have both doors open at the same time!!
|The photohelic gauge controls the upper and lower pressure limits in a glovebox. Modern gloveboxes use a solid state controller or touch screen interface, but the function is the same. If the pressure in the box gets too high, the controller automatically opens a valve to the vacuum pump to relieve the excess pressure and prevent the gloves from blowing off. Likewise, if the pressure is too low, the controller fills the box with nitrogen. You can set these upper and lower limits by turning the two small knobs below the gauge. The two red needles on the gauge indicate the current settings and the black one (coincident with the lower setting in this photo) indicates the current pressure.|
Having the glovebox at a negative pressure with respect to the atmosphere is a Bad Thing because air will be drawn into the box through any small pinholes or leaks. Therefore, one tends to operate a glovebox at a slight positive pressure (i.e. both the cutoffs should be to the left side of zero).
|The pedatrol is a foot pedal that allows one to manually adjust the pressure inside the glovebox. The high and low limits set on the photohelic gauge still apply, but you can use the pedatrol to open the box to the vacuum pump or the nitrogen supply to get the pressure to a comfortable working level.|
Notice that the pedatrol is sort of like a two-button computer mouse. Pressing on the left side decreases the pressure in the box and pressing on the right side increases it. No, you can't press both sides at once!
The gloves are obviously an important component of the glovebox. The gloves on a glovebox are usually sized large so that anyone can get their hands in. This makes life a bit difficult for people with small hands, but one quickly learns how to deal with oversized gloves.
The biggest threat to the atmospheric integrity of the glovebox comes from pinholes and cuts in the gloves. The most common ways of damaging the gloves involve the use of razor blades, copper wire (sharp ends), syringe needles and scissors inside the box. If you do use any of these BE EXTREMELY CAREFUL!! Gloves are rather expensive and replacement is required if there are more than three or four pinholes on either glove (depending on size).
On a research grade glovebox, the atmosphere is purified to less than 1 ppm H2O and less than 5 ppm O2 by circulating it through a catalyst bed (also