PREPARATIONS 87Then collect 5-6 gas-jars filled with the acetylene, and carryout the following tests.(1)Odour.The gas collected in this way has a somewhatonion-like odour, which is much less pronounced than that of thecrude gas given off directly from the carbide without subsequentpurification. Absolutely pure acetylene, however, is almostodourless.(2)Bromine.Slip the glass cover of a jar momentarily aside,add 2-3 ml. of bromine water, replace the cover and shake thecontents of the jar vigorously. Note that the bromine is absorbedonly very slowly, in marked contrast to the rapid absorption byethylene. This slow reaction with bromine water is also inmarked contrast to the action of chlorine water, which unites withacetylene with explosive violence. (Therefore do not attemptthis test with chlorine or chlorine water.)(3)Alkaline Permanganate.To another jar add similarly2-3 ml. of very dilute potassium permanganate solution con-taining sodium carbonate. On shaking the jar the permanganate
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