The genuineness of rose oil is generally judged by its odor, its capacity of congealing, and the manner of its crystallization. The odor is by all means the most reliable criterion, but requires much experience, and especially reliable pure standard samples for comparison. The capacity of congealing at certain conditions of temperature, is, to be sure, also a requirement of genuine rose oil, but, as previously mentioned, this property varies very much, and is subject to different influences, so that a fixed standard at which pure rose oil must congeal cannot be established. Attention must, however, be called to the fact that the quality of a rose oil does by no means rise with its greater capacity to congeal, since only the liquid oxygenated portion possesses odor. Schimmel & Co. bring at present into commerce a liquid rose oil freed from stearoptene which can be highly recommended for finer alcoholic perfumes. It remains fluid at 32° F., but in a cold mixture congeals to a gelatinous mass, and hence is not absolutely free from stearoptene. It has an extremely fine and powerful odor, and when dissolved in alcohol does not give the disagreeable crystalline separations of the ordinary rose oil, which produce a disturbing effect, especially in the preparation of extracts. For the insulation and determination of the stearoptene in rose oil, Schimmel & Co. proceed as follows: Heat 50 grammes of oil together with 500 grammes of 75 per cent. alcohol to from 158° to 176° F. In cooling, the stearoptene separates nearly quantitatively. Separate it from the fluid, treat it again in the same manner with 200 grammes of 75 per cent. alcohol, and repeat the operation until the stearoptene is entirely free from odor. Two treatments of the crude stearoptene are generally sufficient. In this manner Schimmel & Co. obtained from 1887 German rose oil 32½ per cent. stearoptene, from 1888 German rose oil 34 per cent., from 1887 Turkish rose oil 12 to 13 per cent., and from 1888 Turkish rose oil 14 per cent.