A CLOSE relation exists between the effect of scratching the wall of a glass container with the tip of a glass rod and the nature of the liquid present. Ordinary round-bottomed 5-ml. test tubes are half filled and the inside wall briskly scratched some fifty times. The result is examined under proper light, the contents stirred, allowed to settle overnight, and the sediment examined. Three types of effect are observed. (1) The rod slips. This is caused by aromatic compounds (except benzene and some simpler derivatives); some other cyclic compounds; open-chain compounds of more than ten carbons approximately. (2) The rod bites and produces glass dust, varying in amount and texture, which immediately disperses. This is caused by non-polar compounds of low weight, most ketones, and sulphuric acid. (3) The rod bites and produces abundant dust which sticks most characteristically to the wall, on which it can be smeared. This is given, in decreasing order, by : (a) water and monohydroxyalcohols; (b) dihydroxyalcohols, primary amines; (c) aliphatic acids, some esters, aldehydes, ketones, secondary amines. This last group is intermediate between (2) and (3).