The dietetic value of coffee depends principally upon the alkaloid caffeine or theine which it contains in common with tea and cocoa or chocolate. Good coffee contains nearly one per cent. of this substance. When obtained in a pure state it crystallizes in slender needles. The peculiar aroma of coffee is due to the presence of caffeone,[18] which develops in the process of roasting. It may be isolated as a brown oil, heavier than water, by distilling roasted coffee with water. The roasting of coffee is an operation requiring much good judgment, for by carrying the process beyond a certain point the aroma is destroyed and a disagreeable flavor is produced. Roasted coffee when ground quickly deteriorates unless kept in close vessels. Mocha coffee, which is brought from Arabia, is the best, and that from Java ranks next. Much of the so-called Mocha coffee is raised in Brazil, or elsewhere, and shipped to Arabia, after which it finds its way into the markets. The berries of the true Mocha coffee are small, dark and yellow; those of Java are a paler yellow, while the West India and Brazilian coffees have a greenish-gray tint. The last named coffee is usually sold under the name of Rio, an abbreviation of the leading coffee exporting port of Brazil, namely, Rio de Janeiro; Martinique and St. Domingo coffees are two other kinds but little known. Coffee is principally valuable for its stimulating effects upon the system. It produces a buoyancy of feeling, lightens the sensation of fatigue, and sustains the muscles when under prolonged exertion. A cup of rich, hot coffee seems to infuse new life into an o’er-tired body. Equally with tea it is “the cup that cheers, but not inebriates.” “Coffee which makes the politician wise And see through all things with his half-shut eyes.” Coffee is the subject of many adulterations, usually when sold in the ground state. Several kinds of seeds resembling coffee in size have been employed to adulterate the whole coffee, some of which need to be colored before they will pass for the genuine. Many kinds of roots are sliced, dried and roasted for the adulteration of coffee, among the leading ones of which are chicory, carrot and the beet. Spent tanbark and even dried beef’s liver have been thus employed. Many of these fraudulent additions can be detected with the microscope. Ground coffee floats on water, while most of the adulterations will sink or discolor the water. There is said to be a machine in England for making false berries out of vegetable substance.