This section is from the book "A Treatise On Beverages or The Complete Practical Bottler", by Charles Herman Sulz. Also available from Amazon: A Treatise On Beverages.
Pure attar of roses when distilled with due care is at first colorless, but soon takes a yellowish color. A characteristic property of the oil of rose is, that when it is kept in a cool place, even in summer, it is not liquid, but solid, and must be liquified by the aid of warm water before it can be used. No certain method is known to detect falsification. Admixtures of alcohol for the purpose of increasing the freezing capacity, or admixtures of spermaceti, neither of which, at least in the wholesale trade, is now re-sorted to, are, of course, easily detected. But the most important falsifying medium is oil of geranium, which some dealers order even at Constantinople to be sent to Kyzanlik, to be distilled over again with rose leaves, and to mix with attar of roses. Moderate additions of this oil defy detection. The surest method of testing is by smell, but it requires much training, and can only be acquired by many years' patience. It is still a widespread belief, although an erroneous one, that the quality of the attar of roses corresponds exactly with the degree of its freezing capacity. The "stearopten," which is the freezing agent of the attar, is devoid of any smell whatever, and has, therefore, no bearing on the flavor or the purity of the attar. A certain freezing capacity is, it is true, one of the claims which one may lay on really good attar, but this only because the admixture of other essential oils has the effect of lowering the freezing point. The congealing and fusing points vary to some extent; the former is given at between fifty-two degrees and sixty-three degrees Fahrenheit, according to the quantity of stearopten contained in it; it sometimes, but exceptionally, congeals at a higher temperature; it then shows feathery, transparent crystals, filling all the liquid; the latter is given as lying between 61° and 65° F.; for English oil of rose, as high as 91° F.; for German 99.5° F.
Attar made in the highest-situated villages is, as a rule, considered of greater freezing capability, and of more intense, but harsher flavor, whereas the product from the plain shows a lower freezing point, and is possessed of a sweeter and finer flavor.
Oil of rose has a neutral reaction to test-paper, but Zeller found it to have an acid reaction.