Laboratory Acid Cleaning Bath GILBERT E . MOOS Celanese Corporation of America, Newark, New Jersey
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ABORATORIES which are not large enough to warrant the purchase of a large and expensive stoneware acid cleaning bath will probably find the following unit helpful in cleaning glassware, especially if engaged in research on resinous materials. Alkaline cleaning baths have been proposed1 because of the danger involved in heating chromic acid cleaning solutions; however, hot chromic acid cleaning solutions are still preferred cleaning media, especially for sticky resinous residues which are frequently highly resistant to alkaline cleaning solutions. The apparatus described below was evolved from the need for thoroughly cleaning many thick-glass narrow-mouth bottles, multi-way stopcocks, still-heads, plate-glass, and other oddshaped glass apparatus contaminated with resinous materials which were refractory to alkaline cleaning solutions and rinses of acid cleaning solutions. A discarded iron stool was sawed off to a height of 81/pinches and placed on a piece of transite board in turn placed on a piece of 1-inch asbestos resting on a standard soapstone laboratory bench. Two layers of asbestos hoard were placed on the seat of the stool, and an enameled 51/rgallou pot was placed on the asbestos board. Two more layers of the asbestos board were placed inside the pot, and a 41/2-gallon Pyrex jar (12" X 12") was placed on the asbestos in the pot. A standard dichromate cleaning solution was prepared2 using technical sulfuric acid. A piece of plate glass was placed on top of the Pyrex jar to limit most of the vapors of the hot solution to the container, leaving a small space between the glass plate and the inside edge of the jar to prevent any pressure buildup during heating. Two Bunsen burners and a Meker burner have been used to heat the bath. One-inch asbestos board
has been placed around three sides of the stool to localize the heat of the burners. The glass apparatus to be cleaned may be immersed in the acid by means of a long pair of forceps, but preferably i t is suspended by pieces of Nichrome wire, which has a remarkable resistance to the acid cleaning solution. After immersion for a length of time (e. g., 1 to 60 minutes) dependent upon the temperature of the bath as well as the nature and the amount of the resinous residue, the apparatus is removed from the bath with the aid of a pair of forceps when necessary and placed in an enameled tray-adjacent to the bath-to cool before being rinsed off with tap and distilled water. (In certain cases the glassware is rinsed with dilute alkali to remove residual acid which is claimed to have a strong affinity for g l a s ~ . ~ ) This unit has .worked satisfactorily for about a year, the only maintenance being additions of 25 to 50 grams of chromic anhydride infrequently and about a liter of concentrated sulfuric acid once. If the Pyrex jar should break, the enameled pot will safely hold the cleaning solution until i t can be removed. The Pyrex jar is considered to be better than an enameled pot as the immediate container for the acid because enameled ware is prone to cracking, chipping, and even chemical attack by some acids which may be formed in the acid cleaning solution. As a temporary safety container, however, an enameled pot is satisfactoryeven if slightly chipped or cracked. As a substitute for the iron stool, a large standard tripod (e. g., multiple ring variety) would probably serve satisfactorily; or a large electric heater or heaters can be used in place of the stool and gas burners,' as is being done in another laboratory of this department. Five- or six-gallon enameled pots can be purchased a t a cost of four to five dollars, the Pyrex jar for six dollars.
' GADDIS,S., J. CHEM.EDUC.,19, 368 (1942). ' K o ~ ~ x o I.w M., , AND E. B. SANDELL, ''Textbook of Quanti- -
tative Inoreenic Analvsis." The Mamillan Com~anv.New
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WAISBKOT, S. W., Personal communication.
' SHUGAR, G., Personal communication.
