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costs and safety. If there is limited or no success with either of these solvents, try other appropriate solvents.

Preparation. Be sure to remove any soaps or excess water that may be remaining in the glassware.

Use. Always use the lowest grade (Technical) of any solvent when cleaning glassware. Use 10 mL of a higher grade (Reagent) for a final rinse of the glassware. If the solvent has a high boiling point, select a suitable (polar or nonpolar) solvent with a low boiling point for the final rinse to facilitate evaporation.

Safety Consideration. Safety glasses should be worn. Because there is often a high percentage of synthetic fibers in clothing, it is a good idea to wear a lab coat. Many of the organic solvents used in the laboratory could damage your clothing. Organic solvents should not come in contact with skin because they are drying to the skin. Most organic solvents are irritating to some degree to most people. If an organic solvent is trapped against your skin, such as between a ring and finger or absorbed into clothing, the irritation will have a greater time to develop.

Keep in mind that a number of organic solvents are carcinogenic (i.e., carbon tetrachloride and benzene in particular). Some may dissolve rubber gloves, so be careful of that possibility. Always use organic solvents in a fume hood. The vapors of many solvents can have minor to major health dangers. For instance, chloroform is a suspected carcinogen and known to cause liver damage. Chloroform used to be used as an anesthetic by putting patients to sleep. With improper ventilation, one could pass out from the vapors. Most organic solvents are flammable and should therefore be kept far from any open flame, sparks, or high heat sources.

Disposal. Acetone and alcohol can be saved for future cleaning, or recovered by distillation. None of the halogenated hydrocarbons should ever be poured down the sink. If poured on a rag to wipe a stopcock, you may be able to leave the rag in a fume hood to dry before disposing of the rag. However, such a rag may classify as a toxic waste and may require special handling and disposal. There are many laws that govern the disposal of organic solvents, so check with the safety coordinator where you work for specific information.

4.1.7 The Base Bath

The base bath seems like an ideal cleaning method. You carefully lower your item to be cleaned into the bath, let it soak for a period of time (about a half hour), take it out, rinse it, give it an acid rinse, rinse it in water once again, then give it a distilled water rinse. The base bath is the preferred method of cleaning when silicone stopcock grease is used, as it effectively removes that type of grease better than any other cleaning method.

However, there are disadvantages to the base bath. First, it has some safety hazards. The alcohol is a potential fire hazard, and the bath's alkalinity is caustic to skin. The base bath is also a mild glass stripper. That is, instead of cleaning the glassware, it actually removes layers of glass (and any adjoining contamination).

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hydrocarbon solvent (for example, dimethyl chloride) should be sufficient before a base bath soak. If there is a fluorinated grease (such as Krytox) mixed with the silicon grease, see Sec. 3.3.3 for some suggestions on cleaning prior to any subsequent high-heating situations.

Safety Considerations. Safety goggles should be worn. A base bath is highly caustic, so rubber gloves are a must. Since the primary liquid of a base bath is alcohol, it is also highly flammable, so the bath must be kept away from open flames, sparks, high heat sources, or anything that could ignite the solution. Because a strong base can dissolve (strip) glassware, it is important not to let glassware sit too long in the base bath.

The long-term effects of glass remaining in a base bath are as follows:

1.An etching (frosting) of the glass could increase the ability of contaminants to "cling" to the glassware. Etching provides more surface area for dirt to cling to. Thus, it is more difficult to remove material from etched glassware.

2.The ability of high-vacuum stopcocks to maintain a vacuum may be lost.

3.The ceramic decals on glassware (including volumetric marks) may be removed.

4.Volumetric glassware is likely to exhibit increased volumes.

Disposal. As a base bath is used, it tends to lose volume both to evaporation and to the small loss incurred each time an object is removed carrying some base bath with it. The remaining base bath can be recharged by adding to it a new solution, so disposal is seldom necessary. If you wish to dispose of the remaining solution, as long as the base has been neutralized (check with litmus paper) and contains no heavy metals, it can be rinsed down the sink. However, check with local environmental and safety laws to see if any other concerns need to be addressed.

4.1.8 Acids and Oxidizers

Organic and carbonaceous materials can be easily removed with acids and oxidizers. In addition, other glass contamination, such as calcium and other alkali deposits, can be effectively removed with hydrochloric acid (HCl). On the other hand, because alkali deposits are removed from glass surfaces with this rinse, there will be a more porous surface on the glass than before the rinse. This greater porosity will mean greater water absorption and possibly greater cleaning problems in the future. This problem is more likely in porcelain containers and soft glass than borosilicate glass.

Pre-preparation. Wipe off any excess stopcock grease with a Kimwipe tissue. Then, clean any glassware covered with organic stopcock grease with an organic solvent. Next there should be the standard general cleaning with soap and water and/or a rinse with an organic solvent.

Material. Hydrochloric acid (HCl), sulfuric acid (H2SO4), nitric acid (HNO3), or chromic acid (Chromerge®) (see the next section).

Preparation. Acids can be used as straight concentrated solutions or diluted to some degree with water. Some can be mixed (i.e., aqua regia: three parts hydrochloric and one part nitric acid). Another mixed solution is peroxysulfuric acid. It is made by mixing a few milliliters (i.e., 5 mL) of concentrated H2SO4 with an equal amount of 30% H2O2. Wanning (by steam) can often increase the effectiveness of an acid or oxidizer.

Use. All acids must be used in a fume hood. Let the acid soak in the glassware for a short (or long) period of time (as necessary). Swirling with a magno-stirrer and/or heating the acid or oxidizer by use of a steam bath (do not use a direct flame) can facilitate the action. Mineral deposits can often be removed by hydrochloric acid. Metal films can often be removed by nitric acid.

After cleaning with an acid or oxidizer and after rinsing with water, it is good practice to use ammonia as a neutralizing rinse. This rinse should be done before a second rinse is made with water, and a final rinse with distilled (or deionized) water. The ammonia neutralizes the acid or oxidizer. However, if you are working with organic compounds, it is better not to do an ammonia rinse because many organic reactions are acid-catalyzed.

Safety Considerations. The use of a fume hood, eye protection, and protective gloves are a must. Lab coats are also recommended because these acids can destroy clothing and they can damage skin. If any acid gets in your eyes, wash them copiously with water and seek medical attention. If you wear contacts, after washing copiously with water, remove the contacts, rinse with more water, then seek medical attention. Do not stop to remove contacts before rinsing with water. The flushing water will probably remove your contacts for you. If you think you might have accidentally spilled any acid on any part of your body, wash copiously with soap and water just as a precaution. If you feel an itching or burning sensation after having worked with acids or oxidizers, wash the area copiously with soap and water. If the itching or burning sensation continues, seek medical attention.

Disposal. As long as the acid does not contain chromium, or is not hydrofluoric acid, it may be washed down the sink after proper neutralization.* Neutralization is done by first diluting the acid with water to less than 1 M followed by adding either solid sodium hydroxide or 5% sodium hydroxide while constantly mixing the solution until the solution is approximately neutral. Any heavy metals that may have been dissolved by the acid must be removed before disposal. The best way to remove the metal is to participate the metal, neutralize the acid, and send the metal participate to a proper waste facility.

*Both chromic acid and hydrofluoric acid disposal are dealt with in Sec. 4.1.9 and Sec. 4.1.10, respectively.