A Compromise Method for Dispensing Some Strong Acids for Qualitative Analysis Classes Dispensing concentrated hydrochloric and sulfuric acids in large qualitative analysis classes, by any means other than giving students individual reagent bottles, of necessity involves compromise. Problems that wauld not arise with careful researchers do occur with large classes where not all of the students are knowledgeable, careful, and considerate. Difficulties encountered with screw-top pint battles of these reagents are spillage, droppers and bulbs in the battles, caps left off (or even lost), and highly discolored reagents. Glass-stoppered bottles may be contaminated when the stoppers are placed on bench tops. Wash bottles may drip and same students find them awkward. Given that some eampromise seems inevitable in a non-ideal world, the one that suggests itself in these circumstances wauld he a small, readily refillable vessel from which students could draw their acid. Avessel, sufficiently small and kept in the hood, would not need to be capped (although it could be) because the acid would not stand in it very long. Droppers cauld not be lost in it. Contaminated acid could be removed, discarded, and replaced. In our laboratories. we use a device that has been satisfactom and that retauires onlv the most rudimentam" elasshlow.ingskills.'l?levessel i s a four-lnoh tedt tuhr. Afiwt-lang8-mmgla*stubers p u t u n a s a s l d r - a m belmv the rn~dpolnt u t t h r test lube and bcnr down, pnmllcl ro thc rest tuhe. Thlr tube is insenrd into a two-hole ruhher sropprr that fits the aeid bottle. A bent elass tube with a rubber bulb is inserted into the other hale. allawine the acid g b e ~ u m o e d carefully into the test tube with the excess draining back into the battle. This second tuhe should be short enough that the weight of the bulb does not topple the bottle and so that the other end cannot be inserted below the surface of the acid. Exposure of the acid to air is slowed by the use of an imperfect eheek-valve. (The imperfection is beneficial in that it allows the bulb to refill without need far a second check-valve and im~erfectianis easv to achieve.) The check-valve mny hr fhhneated in the follmwng way. Asectmn of X-mm tubma approxmxately 6 in.long Ir heatpd in the mlddlr while rotntina the tuhe. l h s causer the glas* to rhwken, ron.itnctma the tube. W h e n the tuhe cools, men a 5-mm l'vrcx bead. B ~ O Winto the tube ion the sideof the constriction where the bead is) and see how eaod a seal is made. Then &eat this operation with the head on the other side of the constriction, noting which is the better (and satisfactory) seal. Place the head in the side ofthe better seal, heat a small spot on the tube about 112 in. above the bead and push the hat glass slightly into the tube and down with the tip of the handle of a triangular file. The indentation farmed will trap the bead where it belongs without affording an opportunity for the bead's forming an unwanted seal. The bottom is then sealed to a 6-in, tube and the top sealed to the test tube. This system is not suitable for nitric aeid because the stoppers decompose. While 6-mm tubing may be sealed to the bottom of the check valve, 8-mm tubing gives a sturdier device.
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Ben Ruekberg University of Rhode Island Kingstown, RI 02881
450
Journal of Chemical Education
