Dr. Hare on the Sugar of the Sweet Potato. 285 



SM-O 



— = vol. of oxygen in the carbonic oxide." 



This method is evidently preferable in the case of a mixture 

 known to consist of pure bihydroguret and carbonic oxide: 

 but unfortunately it is inapplicable if hydrogen be present in 

 any other state than as a definite compound with carbon, re- 

 quiring twice its volume of oxygen for saturation. The pro- 

 cess of Dr. Bache is not competent to inform us what the 

 gases are ; but enables us, when their nature is known, to 

 discover their proportions. 



Art. VI. — Oil the Saccharum of the Sweet Potato {Convol- 

 vulus battatas ;) by Robert Hare, M. D., Professor of 

 Chemistry in the University of Pennsylvania. 



Dr. TiDYMAN, of South Carolina, lately supplied me with 

 some sweet potatoes, of a kind in which sweet matter is pe- 

 culiarly abundant, and requested that I would ascertain if 

 there were any sugar in them. Having pared, and by means 

 of the instrument used for slicing cabbages or cucumbers, 

 reduced them to very thin slices ; about a pound was boiled 

 in alcohol of the specific gravity of .845, which appeared to 

 extract all the sweetness, yet on cooling yielded no crystals 

 of sugar. The solution being subjected to distillation, till 

 the alcohol was removed, an uncrystallizable syrup remain- 

 ed. In like manner, when aqueous infusions of the potatoes 

 were concentrated, by boiling or evaporation, the residual 

 syrup was uncrystallizable. It appears therefore that the 

 sweet matter of this vegetable is analogous to molasses, or 

 the saccharum of malt. 



Its resemblance to the latter was so remarkable, that I 

 was led to boil a wort, made from the potatoes, of proper 

 spissitude, say s. g. 1060, with a due quantity of hops, about 

 two hours. 



It was then cooled to about sixty-five degrees, and yest 

 was added. As far as I could judge, the phenomena of the 

 fermentation, and the resulting liquor, were precisely the 

 same as if malt had been used. The wort was ke[)t in a 

 warm place until the temperature 85 F. and the fall of the 

 head showed the attenuation to be sufficient.* Yest sub- 



* In passing to this state, there should be a loss in gravity of about four per 

 cent. 



