Capillary Tube Flame Test An interesting alternative for nichrome wire flame tests of solutions containing Sr2+,CaZ+,Ba2+,Na+, and Kt is to use a capillary tube. The method involves drawing a 1.5-1.8- by 1M1-mm capillary tube as if you were preparing to spot solutions in paper chromatography. The solution t o be tested is drawn into the capillary tuhe. The tube is held approximately 2 mm away from the base of a cool flame a t an angle of 4 5 O t o the horizontal. The heat of the flame vaporizes the solution in the tip of the capillary tuhe causing it to inject into the flame. Liquid higher up in the tuhe does not vaporize, and the liquid's greater mass and higher viscosity keep it stationary. After the vapor has left, capillary action draws the solution hack down the tuhe to be vaporized and injected into the flame. With some practice, and by adjustment of both the flame and capillary tuhe position, a continuous stream of vapor can be injected into the flame. The caoillarv-tube method has two advantaees over the more conventional nichrome wire method. The first is cost. Fnrm my expwirnce in the t'reshmen chemistry lab. I would pstlmate the average quantity olreagent grade HCI used fur cleaning the nichromp wire m be 211 ml,at arusl ot 50.17 per use.Cspillsry tut,rs,on the other hand,cost $(I 025each. With each capillar). tuheyieldmg tuoruller ruitablt, ior tlnme tests, the student can o w 14 t u h e s t d w r thecost d?Omli,f HC'I is reached. The second advantage concerns ventilation. Because HCI is used t o clean the nichrome wire, adequate ventilation ia needed to remove the HC1 vapor that is generated. This problem does not exist with the capillary-tube method. Each tuhe is used for only one solution, and then discarded; HCI is not used. ~~
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John H. Boucher BOX 556 Hamilton Hall UNL Lincoln. NE 68508
158
Journal of Chemical Education
