324 PRACTICAL ORGANIC CHEMISTRY gauze) into a small quantity of the powdered organic compound, e.g.y chloral hydrate. Now insert the wire into the vertical edge of the flame about one inch from the top of the burner. A bright green coloration, often lasting only a few seconds, indicates halogen in the organic compound. This test depends on the hot copper oxide decomposing a small quantity of the organic compound with the formation of the corres-ponding copper halide, which, being volatile at high temperatures, gives the usual green copper coloration. A few halogen-free amides, such as urea, thio-urea, and some pyridine compounds, give volatile cuprous cyanide under these conditions, however, and therefore also give the green coloration. It can be said therefore that a negative result for halogen is decisive, whereas a positive result means that halogen is probably present. The great value of this test for halogen is that,
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