On the dried Coffee-leaf of Sumatra. 21 



ployed by M. Carnot in his theory of the motive power of heat, 

 although founded on contrary principles, and leading to diflFerent 

 results. 



Carnot, in fact, considers heat to be something of a peculiar 

 kind, whether a condition or a substance, the total amount of 

 which in nature is incapable of increase or of dimimition. It is 

 not, therefore, according to his theory, convertible into mecha- 

 nical power ; but is capable, by its transmission through sub- 

 stances under particular ciixum stances, of causing mechanical 

 power to be developed. He supposes a body to go through 

 certain changes of temperature and volume, and to return at last 

 to its primitive volume and temperature, and conceives, in accord- 

 ance with his view of the nature of heat, that it must have given 

 out exactly the same quantity of heat that it has absorbed. The 

 transmission of this heat he regards as the cause of the produc- 

 tion of an amount of mechanical power, depending on the quan- 

 tity of heat transmitted and on the temperature at winch the 

 transmission has taken place. According to these principles, a 

 body, having received a certain quantity of heat, is capable of 

 giving out not only all the heat it has received, but also a quan- 

 tity of mechanical power which did not before exist. 



According to the theory of this Essay, on the contrary, and 

 to every conceivable tiieory which regards heat as a modification 

 of motion, no mechanical power can be given out in the shape 

 of expansion unless the quantity of heat emitted by the body in 

 returning to its primitive temperature and volume is less than 

 the quantity of heat originally received ; the excess of the latter 

 quantity above the former disappearing as heat, to appear as 

 expansive power, so that the sum of the vis viva in those two 

 forms continues unchanged. 



[To be continued.] 



II. On the dried Coffee-leaf of Sumatra, which is employed in 

 that and some of the adjacent Islands as a substitute for^ Tea^ or 

 for the Coffee-bean. By John Stenuouse, LL.D., F.R.S."^ 



I RECENTLY received from my friend Daniel Hanbury, Jan., 

 Esq., a quantity of dried coflee-leaves which had been pre- 

 pared in Sumatra, under the direction of N. M. Ward, Esq. of 

 Padangt. The sam])le had a deep brown colour, and consisted 

 of the leaves of the coffee-tree mixed with fragments of the 

 stalks. The leaves had been very strongly roasted in rather a 

 rough manner, and had consequently acquired a slightly empy- 



* Communicated by the Author. 



t Sec a paner by Mr. llaubury in the 13th volume of the Pharmaceutical 

 Journal, p. 2O7. 



