Of the Excellent Qualities of Coffee. 623 



air which is shut up within the box (between the 

 piston and the cover) might be well confined. 



Before I proceed to describe the apparatus I shall 

 recommend for making coffee, it will be useful to in- 

 quire what the causes are which render the prepara- 

 tion of that liquor so precarious ; and, in order to 

 facilitate that investigation, we must see what the cir- 

 cumstances are on which the qualities depend which 

 are most esteemed in coffee. 



Boilins: hot water extracts from coffee which has 

 been properly roasted and ground an aromatic sub- 

 stance of an exquisite flavour, together with a consider- 

 able quantity of astringent matter, of a bitter but very 

 agreeable taste ; but this aromatic substance, which is 

 supposed to be an oil, is extremely volatile, and is so 

 feebly united to the water that it escapes from it into 

 the air with great facility. 



If a cup of the very best coffee prepared in the 

 highest perfection, and boiling hot, be placed on a 

 table in the middle of a large room, and suffered to 

 cool, it will in cooling fill the room with its fragrance ; 

 but the coffee after having become cold will be found 

 to have lost a great deal of its flavour. 



If it be again heated, its taste and flavour will be still 

 farther impaired ; and after it has been heated and 

 cooled two or three times it will be found to be quite 

 vapid and disgusting. 



The fragrance diffused through the air is a sure in- 

 dication that the coffee has lost some of its most vola- 

 tile parts ; and as that liquor is found to have lost its 

 peculiar flavour, and also its exhilarating quality, there 

 can be no doubt but that both these depend on the 

 preservation of those volatile particles which escape 

 into the air with such facility. 



