22 



similar to the volatile oil in tea ; but the quantity of 

 it in coffee appears to be comparatively very small ; for 

 whilst 100 Ibs. of tea-leaves contain 1 Ib. 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 gene- 

 rated 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 100Z. 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 , ., r . 3'64 ..... 10-42 

 Extractive .... 0'62 . 4.80 



Eesin 0-411 



Fatty oil 0'52 J 



Solid residue . . . . 66-66 , 6875 

 Loss 10-57 1-45 



100-00 



" The examination of coffee," observes Dr. P. 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: 



