A Test Tube-Heating Unit for Use in Semimicro QualitativeAnalysis The heating (unit shown in the photograph is used hy our students in t h ~ semimicro qunlltative analyris course in chemistry. W e use thioacrtamide solution to effect sulfide precipitation in the copper-arsenic group, and the procedure1 requires heating of the reaction tuhe in a boiling water bath. The unit is relatively carefree both from the student and lab management view, and it may be used whenever i t is necessary t o beat reaction tubes. Its compactness allows it to be stationed in a hood without taking up too much room. It is especially preferred when hydrogen sulfide or other poisonous and flammable gas is generated. The unit sits about 2 cm off the surface, and so air flow in the hood is not impeded. A heating mantle (such as VWR 33152.180, or larger) filled with clean sand is all that is required. As a convenience we supply each student with an aluminum plate (apprax. 2'/a in.z X %a in.) with four holes that accept 13- X 100-mm test tubes. Four flanges bent a t right angles to the surface ofthe plate are pushed into the sand to hold the plate in position. Students write their names on the plate with a marking pen, and so each set of reaction tubes is identifiable. I If the annd ir held at about 130 O C , rapid heating occurs, and this saves time. l n a d d i t i m s p i l l ~ ohail-oversarrrontnined r in the rwd,which may he replace4 ns.,ftrn :,: 1s nwc.i,r\ I t mr w i h c i m protect the imide of the heating mantlp further, a linrr of high-density p d y e l h \ l ~ n r1 1 1 8 ~Ilt u.ed, pr.0, iuc4 thdt the operating temperature is reduced t o about 100 'C. ~
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Sorum, C. H.: Lagowski, J. J. Introduction to Semimicro Qualitatiue Analysis; Prentice-Hall: Englewood Cliffs, NJ, 1983; p 191. John M. DeMoura Univerrity of Idaho
MOSCOW, ID 83843
626
Journal
of Chemical Education
