About 200 oil cells may be counted in one transverse section, so that the large amount of essential oil in the drug is well shown by its microscopic character. Pollen grains and sometimes whole anthers are present and concretions of oxalate of lime.
The fibro-vascular bundles, as well as the tissues bordering on the oil cells, assume a greenish-black hue on coming in contact with alcoholic perchloride of iron. Oil cells are largely distributed in the leaves and petals but no starch is found in them.
The clove is very rich in essential oil, containing a greater proportion than any other plant. The oil has a greater specific gravity than water and, therefore, sinks in it. Water extracts very little of the flavor of cloves. The oil combined with resinous matter in cloves gives them their pungency, and their aromatic property depends on the amount of oil they contain.
In studying the structure of both the whole or the powdered cloves, an examination for starch in the powder should first be made in water, as the starch granules swell by the use of the chloral-hydrate solution. This solution must be used, however, as the sections and fragments will not be transparent without it.
Cloves are ground on common burr stone, but great care must be taken in grinding since they contain so much oil. The best powdered cloves present a rich meal of reddish-brown color and are a good preventive of moths, but they deteriorate very rapidly. The natives of China and India use cloves to flavor their rice; the oil is also used for medicinal purposes. Cloves, stems, and leaves are shipped in large quantities from Zanzibar for adulterating the powdered clove and are called “vikunia”; by the native, “swahil”; French, “griffers de girofle,” “peduncles de girofle”; Italy, “fustiand bastoreni”; Latin, “stiptes caryophylli.” They form a dull, gray-colored powder and yield only 5 to 6 per cent. of volatile oil, and, of course, have only a corresponding percentage of the strength or value of the true clove (the root yields 0.04 per cent.). On account of their near appearance in color and flavor to the powdered clove, and particularly for their cheapness, they are much sought for by the miller of spices, as he can thus sell his mixture at a price much below the market value of the true powdered clove. This adulterant may be easily detected by the microscope, which will reveal their thick-walled, hard, flinty stone cells and long, yellow, fibrous tissue, as similar structures are not found in the cloves in such abundance. The fruit of the clove, if added, contains starch granules, which are not present in the meal of the leaves and stems. Often the essential oil is pressed from the whole cloves and they are then rubbed in oil between the hands and mixed with cloves which drop from the trees; both are then mixed with good cloves, and all are sold as prime stock. They are, however, easily detected by their pale color and shrunken appearance and lack of pungency. On one occasion several bags of artificial whole cloves arrived in London from Zanzibar, neatly manufactured by machinery from soft deal wood stained a dark color and soaked in a solution of essence of cloves to give them the required scent. Upon investigation it was found that this manufactured article had been imported into Zanzibar from America.
A great many flowers of plants contain the flavor or perfumes of cloves. Among these are the flowers of the lettsomia bana-nox, called by the natives of Bangal “kulmiluta.” The flowers which are produced in rainy seasons are large and pure white, expanding at sunset with a strong flavor of cloves, but they wither at sunrise. Sometimes the flower buds of Dicypellium caryophyllatum of Brazil, which has a bark called clove cassia, are used as substitute for cloves (also called Brazilian clove bark).
Cloves are largely adulterated with roasted rye and when the price of cloves is high, pimento or Jamaica pepper is often used as a mixture. This adulterant may be detected by the microscope by reason of the thick walls of the cells, which are not present in cloves, as well as by the quantity of starch granules which are not visible in the ground clove.
The essential oil of cloves is a mixture of two oils, one a hydrocarbon isomeric with oil of turpentine and the other an oxygenated oil eugenol or eugenic acid, which possesses the taste and odor of cloves, depending on the amount of eugenol it contains. This amount may be estimated by separation as follows: Shake three parts of the oil with a solution composed of one part caustic potash or soda in ten parts of water; press the crystalline paste of eugenol alkali which forms; take off the press residue with water; decompose with hydrochloric acid; wash the liberated eugenol with water, dry it with calcium chloride and then rectify.
Clove oil is often adulterated with phenol. This adulterant may be detected by shaking the oil with fifty times its volume of hot water; after cooling, it is decanted and concentrated at a gentle heat to a small bulk; then a drop of liquid ammonia and a pinch of chloride are dropped on the surface; if phenol is present the liquor will assume a green color, which changes to a blue shade, which will remain for a number of days; if not adulterated, no coloration will be produced. Clove oil is first colorless, or yellow, and darkens with age and by exposure to the air. It consists of sesquialteral and an oxygenated oil, the first passing over with vapor of water, called “light oil of cloves.”
When the crude oil is distilled with strong potash of lye, its composition is C15H24, specific gravity 0.190 at 15 degrees C., its boiling point 251 degrees to 254 degrees C., its optical power being very light.