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 C_{15}H_{24}, specific gravity 0.190 at 15 degrees C., its boiling point 251 degrees to 254 degrees C., its optical power being very light. The other, which is the eugenol, is the chief constituent. Its composition is C_{10}H_{12}O_{2}. This constituent exists to the extent of 76 to 85 per cent., while very fine may contain 90.64 per cent. in the oil of cloves, in direct proportion to the quality of the product.