1.1.13 Limiting Broken Glass in the Lab

1.1.14 Storing Glass

When not in use, glassware should be cleaned and put away. Glassware that is scattered on benchtops and out in the open clutters working areas, is easily broken, will not stay clean, and, if dirty, may be confused for clean glassware. In other words, glassware that is not cleaned and put away is a toxic and/or physical danger that is likely to undermine and potentially negate any viable research. There is a phenomenal amount of wasted glassware and research solely due to glassware that was not cleaned and put away. The techniques of cleaning glassware are discussed in Chapter 4.

Once cleaned, glassware should be dried before it is placed in storage. If possible, a section in your lab should be reserved for cleaning and drying glassware so that you (1) do not contaminate glassware with cleaning materials, and (2) do not have glassware that is drying be in your way.

The best place to store laboratory glassware and equipment is in covered or enclosed storage areas. Open shelving and other areas where dust can settle on (and in) apparatus should be avoided. Glass enclosed storage cabinets are excellent as they provide opportunity for visual inspection of available items and reduce unnecessary door opening. Place strips of tape across large glass doors to prevent accidents by people who may not see the glass.

The most common place for glassware to be stored is in a drawer. Drawers provide many of the recommended requirements for glassware and equipment storage except visibility. In fact, a drawer's biggest liability is that it can be opened and closed quickly by someone trying to locate a particular item. The rattling of glassware rolling into other glassware or apparatus portends glass repair.

There are several ways to protect glassware stored in drawers:

1.Label all drawers. Self-sticking labels are sufficient for most labs. However, if the contents of the drawers are constantly being transferred, metal or plastic card holders may be more practical.

2.Encourage users of the lab not to jerk drawers open or slam them shut. I do not know of any way to prevent these actions, but continued abuse may be thwarted by demanding financial remuneration of broken glassware (if the culprit is caught).

3.Limit free movement of glass items, (a) Small items should be kept in small boxes with cut-off tops (to facilitate observation of the contents), (b) Line drawers with plastic mesh or plastic bubble packing material to limit movement as well as cushion impact against the walls of the drawer, (c) Be sure to prevent items from twisting or tilting within the drawer. Such movement may cause part of an apparatus to stick up and either prevent the drawer from opening or be broken off (if the drawer opener is strong and persistent).

Nesting glassware is a good space saver, but be sure there is adequate room for the glassware to nest. Evaporation dishes are not a problem, but the pour spouts of small beakers tend to wedge within larger beakers.

Obviously the best solution to prevent this situation from happening is to ensure adequate room for smaller beakers. A simple technique may be used to separate beakers. Squeeze the larger beaker at right angles to the jammed unit (see Fig. 1.9). It does not take a great amount of pressure, but you must remove the smaller beaker as you squeeze. For safety's sake, wear leather or Kevlar® gloves when squeezing glassware. Although the amount of flexure needed is very small, if there is a flaw in the right place, a piece could break in your hand.

Limit dust within glass items such as pipettes by plugging the hole with a Kimwipe or wrapping the ends in a Kimwipe held by a rubber band or tape. Do not tape directly on the glassware because it may be difficult to remove after the tape has aged.

1.1.15 Marking Glass

The permanent marks on glassware are made of a special type of a glass-ceramic that fuses onto glass surfaces above 500°C. They are applied either by a silkscreening process or by decal. Ceramic decals are permanent and will resist most chemical attack. They are susceptible to chemical attack by alkalis and hydrofluoric and perchloric acid, all of which can remove the markings.

Old glassware is used to provide a frosted circular spot for marking the glass. This frosted zone was easier to write on than the ceramic spot, but cost more to manufacture than simply adding a ceramic decal spot as part of the ceramic numbering that is placed on already. The frosting added one more step to the manufacturing process, and therefore it was phased out.

The ceramic white dot on most glassware can be written on by pencils for identification. Although it is not easy to write on glass, there are five techniques that allow one to identify and mark on glass:

1.Alcohol-based pens. These pens, usually fiber-tipped, can write on

Fig. 1.9 Nesting beakers and removing stuck nested beakers.

most surfaces and are water-resistant. They can be removed with any hydrocarbon solvent and will burn off in a drying oven. Although they are not likely to smear from the glass onto fingers, they may. These pens can quickly dry out if not recapped after use. They are available in a variety of colors.

2.Waxed pencil. Like a crayon, waxed pencils can easily write on glass and are subject to the same removal techniques as alcohol pens. They are likely to smear onto fingers and other equipment. They are available in a variety of colors.

3.Soft pencil. The company Schwan - STABILO GERMANY makes a line of pencils that are identified as "All-STABILO." These pencils are so soft they can easily write on glassware. The markings from these pencils can withstand high heat (600 to 700°C) but can be wiped off by the rub of a finger.

4.Titanium writing. Titanium dipped in water (or writing on wet glass) will leave a permanent marking on glass. Although admittedly the markings are not easy to see (only ~ 0.25 mm wide*), they are impervious to hydrocarbon solvents and can resist temperatures up to 1500°C. The markings can be removed with nitric acid.

5.Self-adhesive labels. This method is sort of cheating because you are not writing on glass. Rather you are writing on labels stuck to the glass. The labels can be written on by standard pens and pencils, then placed on any type of glassware. Because they are available in different colors, the labels can assist in separating glassware by type, then specific identifying information can be written on the labels. It is possible to remove these labels by lifting them off, but sticky residue may remain. The residue may be removed by acetone. If you write on the label with an ink pen, the ink may smear or bleed if chemicals leak onto the label.

1.1.16 Consumer's Guide to Purchasing Laboratory Glassware

Laboratory glassware can be expensive. As far as the user is concerned, the chemistry of the glass by the three major companies is equally good. However, considerable ranges of quality can be exhibited in glass quality and items made out of a particular glass. If a glass or the products made from that glass are not acceptable, do not accept the item(s).

Glass companies do not try to make poor-quality glassware, nor are they intent on selling their mistakes. However, mistakes happen and sometimes the mistakes get by quality control. Regardless, the final quality control person is the customer.

*The width is related to the amount of contact surface the titanium has with the glass.

If you receive poor-quality glassware, by working with your supplier and/or the glassware manufacturer, the problem can be resolved.

Faults in glass can include the following:

1.Seeds* are like specs of sand in a glass that did not properly melt. They are particularly susceptible to thermal strain that would not affect regular glass.

2.Bubbles are trapped air within glass. These are more visual than structural problems.

3.Airlines are bubbles that got stretched during the manufacturing process. These are more visual than structural problems.

4.Blisters are bubbles that are very close to the surface and are likely to break open. If they partially break open, they may hold liquids or particulate material that can contaminate current or future work.

5.Cordsf are glass inclusions of a bad melt. They may appear like sections or spots of glass that did not properly melt.

6.Chill mark is a wrinkled surface caused by poor forming in a construction technique called "mold pressing." The bases of graduated cylinders and the bodies of funnels are typically made with this process. This is more of a visual imperfection and does not imply poor manufacture.

There are more companies that make glassware than make glass. Each is dependent upon the glass manufacturing companies to provide glass with a minimum of the problems mentioned above. Ideally, such glass flaws are sorted out before or during the manufacturing process. In addition, there are flaws that can be created during the manufacturing or shipping of glass items. Ideally these problems should be caught before reaching the consumer. However, because a number of manufacturing processes are automated, errors in production may not be caught until complaints start to come in from the field (i.e., you).

No manufacturer can be considered totally dependable. Some manufacturers make some products better than other manufacturers, and they make some items better than other items. Therefore, in addition to the flaws that can be found in glass as just listed, do not accept the following flaws in manufactured glass items:

1. Chipped, scratched, or cracked glass out of the box. There are ample opportunities for these flaws to happen in any lab, so you do not need an early assist from the manufacturer, the warehouse, or the shipper. Because any of these three may be equally culpable in causing physical damage, it is best to not assume who might be to blame. Let the supplier worry about it.

2. New stopcocks or joints that leak. Do not "repair" them by adding more stopcock grease than should normally be required. Such prac-

*This flaw can become a focal point for fracture.