The peculiar essential oil which is generated in coffee in the process of roasting, by the action of heat upon some yet unascertained principle contained in the berry, is also very similar to the volatile oil in tea; but the quantity of it in coffee appears to be comparatively very small; for whilst 100 lbs. of tea-leaves contain 1 lb. of volatile oil, it takes 500 cwts. of roasted coffee to give a similar quantity; and yet it is upon the presence of this oil that the flavour and value of the several varieties of coffee mainly depend. The tannic acid is, by some chemists, also said to be generated only in the process of roasting; others maintain that it is present in the raw bean. The chemical properties of the coffee-berry are altered by roasting, and it loses about twenty per cent. of weight, but increases in bulk one-third or one-half. Its peculiar aroma, and some of its other properties, are due to a small quantity of essential oil, only one five-thousandth part of its weight, which would be worth about 100_l._ an ounce in a separate state. Coffee is less rich in theine than tea, but contains more sugar and a good deal of cheese (casein). Schrader has analysed raw and roasted coffee, with the following result: raw. roasted. Peculiar coffee principle 17·58 12·50 Gum and mucilage 3·64 10·42 Extractive 0·62 4·80 Resin 0·41 } Fatty oil 0·52 } 2·08 Solid residue 66·66 68·75 Loss 10·57 1·45 ------------- | 100·00 “The examination of coffee,” observes Dr. F. Knapp, “has led to interesting results, although they are still defective in pointing out the quantitative composition of the berry.” The following is the composition of the ash according to Levi: Potash 50·94 Soda 14·76 Lime 4·33 Magnesia 10·90 Oxide of iron 0·66 Phosphoric acid 13·59 Sulphuric acid trace Chlorine 1·22 Silicic acid 3·58 ------ 99·98 According to the analysis of Payen, the unroasted coffee-berry has the following composition: Moisture 12·0 Glucose and dextrine 15·5 Nitrogenous matters 13·0 Chlorogenate of caffeine, &c. 3·5 to 5·8 Fatty substances 10 to 13·0 Cellulose and woody fibre 34·0 Mineral substances in ash 6·7 Essential oil ·003 ----- 100·0 Or to define the per-centage more closely, we may put it thus: