The quality of cassia oil is recognized by the taste and odor, especially on heating, and the high specific gravity, in consequence of which the oil sinks in water. According to Hager, cassia oil is frequently adulterated with oil of cloves. This is, however, scarcely probable, the price of oil of cloves being, on an average, higher than that of cassia oil. The latter, however, is frequently adulterated with cheaper thickly-fluid volatile oils, especially with cedar oil. In this case the oil does not dissolve in the above-mentioned proportion in alcohol.
The value of cassia oil is dependent on its contents of cinnamaldehyde. Hence, the establishment of its actual value requires a quantitative determination of its contents of cinnamaldehyde, which unfortunately presents great difficulties. For this purpose Schimmel & Co. proceed indirectly as follows: 75 grammes of cassia oil in a capacious boiling flask are mixed with 300 grammes of a boiling-hot 30 per cent. solution of acid sodium sulphite, whereby cinnamaldehyde-sodium sulphite is immediately separated. The whole is then vigorously agitated and allowed to rest for a short time. (With oils rich in aldehyde considerable heating generally takes place, which must eventually be moderated by the addition of cold water.) Next add about 200 grammes of hot water and heat the whole, with frequent shaking, in the water-bath until the combination of the aldehyde with the acid-sodium sulphite is completely dissolved, and the non-aldehydes in the form of an oily layer float upon the solution of the aldehyde salt. Now allow the whole to cool, then shake twice with ether; first, with about 200 cubic centimeters, and then with 100; combine the ethereal extracts of the non-aldehydes separated by means of a separatory funnel, and filter them into a capacious, previously-weighed beaker provided with a platinum wire, the lower end of which is bent in the form of a spiral. Now evaporate the ether as much as possible, by placing the beaker in hot water. When by swinging the beaker the remaining fluid no longer foams up, allow to cool off and weigh. Now return the beaker-glass to the water-bath for ten minutes, weigh again after cooling, and repeat the operation until the difference between two weighings does not amount to more than 0.3 gramme at the utmost. The weighing previous to the last is taken as the correct one.[6]
The weight of the non-aldehydes thus obtained is deducted from the cassia oil used, the difference giving the content of cinnamaldehyde in the latter.
For example:—
| Used 79.71 grammes of oil. | |||
| First weighing of the beaker after evaporating the ether | 147.55 | grammes | |
| Second | 146.84 | " | |
| Third | 146.58 | " | |
| Tare of the beaker | 128.34 | " | |
| Hence non-aldehydes in the oil | 146.84 grammes. | ||
| Less tare | 128.34 " | ||
| ——— | |||
| = 18.50 grammes. | |||
| Calculated to per cent., 23.1 per cent. | |||
| 100 - 23.1 = 76.9 per cent. cinnamaldehyde. | |||
By accurately following the directions given, the difference between two controlling determinations will be only a few tenths per cent., seldom as much as 1 per cent. For practical purposes, for which alone this method is intended, this is more than sufficient.
According to the reports of Schimmel & Co., all the cassia oil brought into commerce from China was for a considerable time adulterated with resin and petroleum, they having found as much as 30 per cent. of resin in the oil. Such adulteration can be established by the determination of the specific gravity and distilling the oil. Good cassia oil should show a specific gravity of 1.05 to 1.07 at 59° F., and by distillation 90 per cent. of pure cassia oil must pass over. The residue should not solidify after cooling and acquire the character of a brittle resin; it must remain at least thickly-fluid, and under no conditions amount to more than 10 per cent.
Citron oil (oleum citri), from the peel of the fruit of Citrus medica or the citron tree. The oil is prepared in a similar manner to that of oil of bergamot, either by expression or distillation, the latter process yielding more and purer oil.
Rectified citron oil is colorless, of an agreeable penetrating odor and acrid taste, and very sensitive to light and air. By exposure to light it turns yellow, and if air be admitted at the same time, it is first converted into a fluid which, on account of its content of ozone, possesses strong bleaching powers. The oil at the same time acquires a disagreeable odor, resembling that of oil of turpentine, and is finally converted into a resinous mass.