A Safe, Accurate Solids Dispenser and Weighing Aid The most usual method of dispensing solid chemicals in schoollaboratories is t o provide a reagent bottle, a spoon and a balance and allow the student to help himself. This is a slow, messy, wasteful and often downright dangerous operation, The daneer is lareelv due to snilline and snreadineof the chemicals usuallv with skin contact P often with &st inhalation. w i t h many cokmonly used reagents now on the toxic substances list, i.e., chromatea, arsenites and mercury salts, such haphazard dispensing c b must be avoided. These dispensing problems, however, can be largely overcome hy proper use of the dispenser illustrated in the figure. A bottle or Erlenmeyer flask of appropriate size is fitted with astopper which holds in its axisa tubeextending in toahout thevolume center of the bottle and out beyond the stopper one to several inches in length. The bottle, filled less than half full with the solid, is held upside down while holding the outside end of the tube shut with the forefinger. By simply shaking the hottle with an up and down motion, the tuhe may be filled to any chosen level. Removing the finger from the tube end then allows the tube contents to he released into even a narrow opening without danger of spilling. Dusts are largely retained within the dispenser. Tapping the tube may be necessary to dislodge the solid from the tube where the solid is not too free flowing. T o prevent contact of the finger withtoxic chemicals, the outside tube end may be provided with aflap ofplastic or sheet rubber attached by glue or tape t o the tube, and positioned to be pressed against the tube end by the finger. For lab sessions in which a specific quantity is t o be dispensed for each student, the proper length of tuhe t o be filled can be marked on the tube with a grease pencil. More conveniently still, graduated tubing can he used. Broken pieces of Mohr pipet, etc. can serve admirably. When such a graduated tube is used, the hulk density of the solid dispensed can be estimated, for example by carefully dispensing 1ml of the solid and weighing it. The bulk density thus determined and written on the reagent bottle will thereafter serve as a guide t o the proper . . volume t o he taken for any desired weight - of that reagent. An important feature of the dispenser is that when held largely horizontally, the solid is distributed along the length of a narrow tuhe, so that by tapping the tuhe with a finger, the tube contents can be released grain by grain. (Excesssolid in the tuhe returns t o the bottle when dispenser is turned right side up.) This is of great advantage when attempting to weigh toaspeeific weight. With a little practice, andafine grained free-flowing solid, oneeanquickly cometo withinabout amilligram of the chosen weight with little chance of overshoot.
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Narwieh University Northfield. Vermont 05663
Volume 55, Number 7,July 1978 1 455
