space of the oven's room, the fumes could be toxic. At the time of the writing of this book, there are no environmentally safe solutions. Accordingly, those concerned about the environment may be inclined to conclude that there is no justification for using Krytox grease. However, Krytox is the only grease for stopcocks that can be used for very low temperatures (-35°C) to very high temperatures (220°C), has a very high level of chemical inertness, and will not affect elastomers or metals. Thus, there are conditions when Krytox is the only viable alternative.

3.3.4 The Teflon Sleeve

There is one other substitute for stopcock grease on standard taper joints: the Teflon sleeve. These sleeves are like socks for your joints. Because they are made of Teflon, they are not attacked by solvents, alkalines, and most other chemicals. Thus, they are wonderful for items like solvent flasks which are under constant fume or chemical contact. However, they are not capable of maintaining a static vacuum and should not be used for vacuum work. Thin Teflon sleeves are less expensive, but cannot take physical abuse. Heavier Teflon sleeves have a greater initial cost, but can be used over and over.

3.3.5 Applying Grease to Stopcocks and Joints

The concept of "if a little is good, then a lot is better, and too much is just right" is incorrect for the application of grease on stopcocks and joints. Excess grease can spread throughout an apparatus, creating a mess that can affect the work in progress, decrease the potential vacuum and the speed of obtaining a vacuum, and, worse, plug up holes in stopcocks, making them inoperative.

Stopcock grease is applied to the inner member of a joint or stopcock, inserted within the outer member, and then twisted and/or rotated to spread the grease throughout the rest of the ground surface. Applying a mild amount of pressure will facilitate an even application throughout a joint. The colder a joint, the more difficult the grease will be to spread. Lightly heating members prior to assembly will help create an even distribution of grease.

When applying stopcock grease to pieces used on vacuum systems, do not use your fingers because perspiration from fingers can result in slow degassing within the system, limiting your potential vacuum. If the grease is supplied in a flat metal tin or glass jar, use a wooden spatula to spread the grease on the inner piece. Grease that is supplied in a tube (similar to toothpaste) is easy to apply by laying the grease directly on the inner member in lengthwise strips (see Fig. 3.33). Regardless of the method of application, one to two strips is all that is necessary for very small joints and stopcocks (14/35 joints or 2-mm stopcocks), and up to four strips are merged for large joints or stopcocks (45/50 joints or 10-mm stopcocks).

Once the grease is applied, insert the inner member into the outer member, twist and/or rotate the inner piece until there is a thin, smooth film of grease between

minute at most. After heating, remove the item from the flame and try to separate the pieces immediately. If this method fails, you may let the piece cool and try again. However, your chance of success goes down rapidly if the first attempt is a failure. In lieu of a flame, one can also point the steam from a steam line at the stuck item. This is obviously safer than the flame and can be used near flammable materials. However, it is somewhat less successful than using an open flame.

Electrical Conduction Heat. If the item is soft glass, such as the ground stopper section on a storage container (or even a perfume bottle), a softer heat is required. This heating can be done by wrapping bare copper or nichrome wire (18 gauge) tightly around the joint, leaving an inch or so of tail. If you heat the wire tail with a flame, conductance will heat the joint. If you wish to use a voltage regulator (such as a Variac®) to heat the wire, use nichrome wire that is insulated with nonflammable covering. Do not use copper because it does not have enough resistance (while trying to get the wire hot, you will draw too much current and likely blow a fuse), and make sure that the wires do not overlap. In addition, be sure to turn the Variac off before handling. The steam mentioned above can also be used on soft glass.

Chemical Soaking Solutions. If it is not possible to use the heat from a flame, there are a few soaking solutions that may help. Their chemical mixtures are as follows3:

Solution #1

Alcohol (2 parts)

Glycerin (1 part)

Sodium chloride (1 part)

Solution #2

Chloral hydrate (10 parts)

Glycerin (5 parts)

Water (5 parts)

25% Hydrochloric acid (3 parts)

Soak the frozen joint or stopcock in either solution overnight or longer. Try to free the item with a moderate amount of force, never an overt amount of force. If either solution fails, try the other solution or either of the methods below.

Soda Pop. Surprisingly, soda pop has been used to successfully separate stuck stopcocks. Some people say you need to use stale cola, others say fresh cola. I've tried both with equally mixed success. Butler,4 using the fresh cola approach, sug-

^Bidymium or AUR 92 glasses are those used by glassblowers. They are obtainable from most of the manufacturers listed in Appendix C, Sec. C.I. Both of these lenses have special filtering properties which eliminate the sodium spectra, allowing the wearer to see through the normally bright yellow light emitted by glass. Sunglasses and welder's glasses cannot be used for substitution.

gested that the mechanism at work is the decomposition of carbonic acid as follows:

H2CO3 -> H2O + CO2

Butler also suggested that it is the resulting CO2 pressure that defreezes the stuck stopcocks. Additionally, he suggested that there may be some interaction between the carbonic acid and various sites on the glass surface. On the other hand, the acidic nature of fresh soda (any fresh soda) is sufficient to dissolve lime and other hard water deposits. Thus, if the joint is frozen due to such deposits*, a fresh soda could ostensibly remove the deposit and defreeze the joint. Despite the loss of a good soda, it would be safer, but probably not as effective, than hydrochloric acid.

Regardless, neither of these suggestions explain why stale cola should work. Whether fresh or stale cola, the joint needs to be soaked from 3 to 48 hours. If you choose to use the fresh cola approach, it should be replenished periodically to allow for fresh acidity and/or bubbles.

Beeswax. Heat the joint to just above the melting temperature of beeswax (about 65°C), then apply the wax at the lip of the two parts. The wax will melt and surface tension will cause the wax to penetrate between the male and female sections. Let cool, then reheat and the joints may separate.

The Vibrating Etching Tool.6 First, remove the carbide tip from an engraving tool (to prevent damaging the glassware), and then place the vibrating end to the ground section while pulling on one of the pieces. You may also try to preheat the joint as mentioned above.

The Crab Mallet. Even if glassware with stopcocks or joints is properly stored in drawers, occasionally the members may stick. The following de-sticking technique will work on dry (ungreased) items only. Use a wooden stick, or crab mallet (see Fig. 3.34), and lightly tap the stuck member in the same alignment as the joint itself (see Fig. 3.35). Be sure to lay the item on a table so that if you are successful, the item will skid on the tabletop a few inches rather than fall to the ground. The use of wood for this technique is important because anything harder is likely to chip, crack, or demolish the glass.

The False Handle. Finally, there may be times when part of a stopcock or plug has broken off, leaving little left to hold onto. This situation can make removal

Fig. 3.34 A crab mallet.

Hard water deposits could happen if assembled glassware is placed in a sink of water and left to soak for an extended period of time.