The chief adulterations are colza and nut oils. The latter is detected by means of the reaction with nitric acid, as described above. Colza oil is recognized by mixing 5 volumes of the sample to be examined, with 1 volume of sulphuric acid of sp. gr. 1.655: if colza or nut oils are present, a brown coloration ensues; under the same circumstances, pure olive oil assumes a pale greenish hue. In case the sample acquires a brown color when treated with sulphuric acid, and a red coloration is produced by the addition of nitric acid, it contains nut oil; if sulphuric acid produces a brown coloration, and nitric acid fails to change it, the presence of oil of colza is indicated.
EXAMINATION OF HEMPSEED OIL.
This oil is frequently adulterated with linseed oil. The reactions exhibited by these oils are nearly identical, and the detection of the admixture is extremely difficult. It is advisable to mix the suspected oil with sulphuric acid, notice being taken of the elevation of temperature produced, and to treat it with nitric acid and with dilute potassa solution, subjecting, at the same time, an artificial mixture of the two pure oils to the same treatment, and comparing the results obtained.
TEA AND ITS ADULTERATION.
Among alimentary substances probably no article is subjected to more adulteration than tea. The sophistications practised may be conveniently divided into three classes:
1. Additions made for the purpose of giving increased bulk and weight, which include foreign leaves and exhausted tea-leaves, and also certain mineral substances, such as metallic iron, sand, brick-dust, etc.
2. Substances added in order to produce an artificial appearance of strength in the tea decoction, catechu, or other bodies rich in tannin, and iron salts being chiefly resorted to for this purpose.
3. The imparting of a bright and shining appearance to the tea by means of various coloring mixtures or "facings," which adulteration, while sometimes practised upon black tea, is much more common with the green variety. This sophistication involves the use of steatite (soap-stone), sulphate of lime, China clay, Prussian blue, indigo, turmeric, and graphite; chromate of lead and copper salts being but very rarely employed. The compound most frequently used consists of a mixture of soap-stone (or gypsum) with Prussian blue, to which a little turmeric is sometimes added.
Genuine tea is the prepared leaf of Thea sinensis. It contains: moisture, 6% to 10%; theine, 0.4% to 4.0%; tannin, (green) 20%, (black) 10%; ash, 5% to 6%; soluble extractive matters, 32% to 50%; and insoluble leaf, 47% to 54%.
