The volatile oils are readily soluble in the ordinary solvents, such as alcohol, ether, chloroform, benzene, acetic ether, carbon disulphide, etc. Mention of this general property is not made in the description of the individual oils. A phenomenon which is sometimes considered as an incomplete solubility may be mentioned here. The turbidity noticed when certain oils are mixed with petroleum ether, paraffin oil') or carbon disulphide may be caused by the small amount of water which the oils have retained from their preparation. The richer an oil is in oxygen, the more water it is capable of dissolving and the more cloudy does it become with petroleum ether.2) The turbidity does not take place when the oil has been thoroughly dried with anhydrous sodium sulphate.

1) Report of Schimmel & Co. October 1898, 41.

Although all oils are readily soluble in strong alcohol, only some of them are entirely soluble in dilute alcohol. For the last class this property becomes a practical and rapid means of examination. The presence of the difficultly soluble turpentine oil can, for instance, be readily shown in this manner in the oils soluble in 70 p. c.3) alcohol. The solubility determination is very simple. Bring into a small graduated cylinder (fig. 72) l/2 to 1 cc. of the oil to be tested and add small portions of the alcohol at a time until with vigorous shaking solution is effected. If an oil which is soluble under normal conditions does not dissolve, it is sometimes possible to draw conclusions as to the adulterant from the character of the turbidity and the separation of the insoluble part. Petroleum floats on the 70 p. c. alcohol, whereas a fatty oil settles in drops at the bottom.

For the examination of volatile oils, alcohol of different percentage strength is used. In the following table the strengths thus far employed are enumerated together with their specific gravities for 15o/15o.4)

1) Cinnamic aldehyde is an exception to this rule. It is practically insoluble in petroleum ether and paraffin oil. Hence cassia oil and Ceylon cinnamon oil dissolve but incompletely in these solvents.

2) When an oil rich in oxygen, such as bergamot oil, is mixed with one rich in terpenes, as turpentine oil or orange oil, the mixture becomes turbid due to the separation of water.

3) The statements in this book always refer to volume percent.

4) According to K. Windisch, Tafeln zur Ermittelung des Alkoholgehaltes von Alkohol-Wassermischungen aus dem spezifischen Gewicht. Berlin, 1893.

Fig. 72.

30 percent by volume d 15o/15o 0,9656

40.............. . 0,9521

50...............0,9347

56...............0,9226

60...............0,9139

62...............0,9094

65 ... ...........0,9025

68...............0,8953

69 percent by volume d 15o/15o 0,8928

70...............0,8904

80...............0,8642

82...............0,8586

85...............0,8499

90...............0,8343

95...............0,8165

98...............0,8040

In order to avoid the necessity of keeping on hand alcohol of different percentage strenght, Dowzard1) has recommended a method which is worth mentioning though it has not established itself. 5 cc. of an oil are dissolved in 10 cc. of absolute alcohol (d15.5o 0,799) and the solution diluted with water from a burette until the solution becomes permanently turbid. By multiplying the number of cc. of water by 100 the "solubility value" is obtained. In connection with bergamot oil, Dowzard determined values between 220 and 290.

The same author suggests the determination of the viscosity-) as a means for examining volatile oils. For the volatile oils, however, this method has never attained practical significance.