364 THE POPULAR SCIENCE MONTHLY. 



of common qualities is to be gained from the external aspect of the 

 plants so brought into use. Between the leaf of the tea-plant and the 

 long pod of the cacao-tree there is no visual resemblance to indicate 

 a common constituent, or to suggest a parallel use. As unlike as their 

 general appearance, even more diverse are the botanical characteristics 

 of the caffeine-containing plants, representing, as they do, diverse fami- 

 lies in the vegetable kingdom. 



In the modes of preparation for use, the sources of caffeine present 

 some coincidences, with many diversities. The coffee-berry, except in 

 some Eastern countries, is roasted, an operation to which its valued 

 fragrance is almost wholly due. The roasting develops from inodor- 

 ous constituents a very diffusible empyreumatic oil of very appetizing 

 odor. In the more elaborate preparation of the tea-leaf 'a degree of 

 roasting appears to be always necessary for development of agreeable 

 flavor, while a certain extent of fermentation precedes the roasting in 

 the manufacture of black teas. For black tea the leaves are withered 

 a little, rolled to liberate the juice, then left in balls for just enough 

 fermentation, then sun-dried, and subjected to a careful firing in a 

 furnace. For green teas the fresh leaves are first withered in hot 

 pans, then rolled to liberate the juices, and slightly roasted in the 

 pans, now sweated in bags, and returned to the pans for a final slow 

 roasting, with stirring for eight or nine hours, beginning at the tem- 

 perature of 160 Fahr. and falling to 120 at the close. These opera- 

 tions are here given as now conducted by the planters in India, and as 

 proposed for tea-culture in the Southern United States, and are con- 

 siderably abridged from the time-established routine of minute detail 

 in China. The teas of commerce contain a distinct essential oil, a con- 

 stituent which does more than all others to obtain the esteem and fix 

 the value of each grade of tea in the market. The question of the 

 effect of the curing process upon the essential oil to liberate or gen- 

 erate or modify or dissipate it is an inquiry of no little interest and 

 consequence, and deserves more chemical investigation than it has 

 received. In the manufacture of all the forms of chocolate, the cacao- 

 seeds, cleared of the shell-coat, are roasted to begin with. Without 

 further treatment they constitute the " cacao-nibs." When ground, 

 pressed to remove a part of the oil, made with sugar into a paste, fla- 

 vored with vanilla, spices, etc., and cast in molds, we have "choco- 

 late " proper. When left in the pulverulent form, or molded in porous 

 and friable cakes, the article is presented as cacao or " cocoa," or 

 "soluble cocoa" the proportion of oil being diminished either by its 

 removal under pressure, or by adding some form of starch or farina. 

 "Flake cocoa" is made by crushing the roasted seed, shell and all. 

 In the preparation of the South American mate, the leaves and twigs 

 are subjected to a " curing " process, and roasted under a covering of 

 earth to develop an aromatic principle which gives flavor to the bev- 

 erage. The guarana, also, is dried or lightly roasted, though acquir- 



