If a rose oil is to be tested, expose the bottle containing the oil to a moderate heat until the contents are entirely liquid; then gently shake the bottle in order to bring about an intimate mixture of elæoptene and stearoptene. Now pour some of the oil into a cylindrical glass flask of 20 to 40 cubic centimeters' capacity and allow it to congeal; then, while heating in the hand, observe how the rigid portions act in liquefying. These rigid, crystalline portions should be transparently clear and, being lighter than the fluid portion, float, while liquefying, in the upper layer of the fluid. Hence, if now the fluid be again allowed to congeal, the crystals should appear within the upper half of the oil. The above-mentioned volatile oils partially lack the property of separating a stearoptene in crystals at from 33.8° to 50° F., and though they may have a rose odor, it is not the mild, fragrant odor of genuine rose oil. To recognize the latter, Guibourt makes use of pure concentrated sulphuric acid. Stir together in a watch-crystal an equal number of drops of the oil and of the acid; pure rose oil preserves its characteristic odor, while the foreign oils exhibit a disagreeable odor even when mixed with genuine rose oil. Schimmel & Co. give a method for an approximate quantitative determination of spermaceti in rose oil: Boil 3 to 5 grammes of stearoptene, separated in the manner above given, with 20 to 25 grammes of 5 per cent. alcoholic potash lye for 5 to 6 hours; then evaporate the alcohol and compound the residue with hot water. In cooling, the greater portion of the stearoptene separates in a crystalline mass upon the surface. Now pour off the alkaline fluid, wash the stearoptene with cold water, then melt it again in hot water, allow it to cool, pour off the water, and repeat the same operations until the wash-water is neutral. The combined aqueous fluids are twice shaken with ether to remove any stearoptene suspended in them. The alcoholic lye separated from the ether is acidulated with dilute sulphuric acid and again extracted with ether. After evaporation no residue (fatty acids) should remain. To control the experiment weigh the regained stearoptene dried at 194° F., adding, of course, the ether used for extracting the alkaline fluid. There will be a small loss, since small quantities of stearoptene always evaporate in drying.