Examination 

 of the vinegar 

 of onion juice 



292 ANALYSIS OF ONIONS. 



as is easy to judge by the action of* oxitnuriatic acid, which 

 venders the alcohol turbid, and communicates to it the pro- 

 perty of forming a copious precipitate with nitrate of ba- 

 rytes. c. After being treated with alcohol the sediment has 

 less smell: it scintillates on burning coals, shrivels, and 

 then swells up, emitting the fetid smell of animal sub- 

 stances, d. Mixed with a solution of sugar, no movement 

 was produced, and no alcohol was formed : whence we may 

 conclude, that this substance is not of the nature of 

 yeast, and not calculated to excite alcoholic fermentation. 



The vinegar formed by onion juice had a yellowish co- 

 lour, a very strong smell of onions, and an acid taste, but 



and the crys- y e t saccharine*. It marked 6° on the areometer for acids: 

 tallizable mat- , • . ., . , . . . .. , , . , 



ter it holds in' out tnis density was owing to a peculiar substance, which 

 solution. gives it the property of crystallizing when it is sufficiently 



conceiitrated. 



This substance, which particularly excited the attention 

 of IVJessrs. Fourcroy and Vauquelin, is neither an acid nor 

 a neutral salt. It presents iVelf in the form of fine, white, 

 acicular crystals, disposed in diverging rays: it has a sac- 

 charine and at the same time acid taste: it is mixed with a 

 gummy matter, and also with citric acid. Hot alcohol dis- 

 solves both the crystalline substance and the acid accom- 

 panying it, leaving the gummy matter untouched. As the 

 alcoholic solution cools, white needly crystals separate, 

 ihining, and arranged in stars. 

 Properties of These crystals have the following properties, a. They 

 the crystals. aTe ^ a svl0W y whiteness, and of a mild, saccharine taste. 

 b. They are equally soluble in water and in alcohol. c. 

 They burn like common sugar, d. Their solution does not 

 ferment with yeast, e. Nitric acid converts them into the 

 oxalic. They afford no mucous acid, unless when they 

 contain mucilage. Our authors satisfied themselves on this 

 occasion, that manna,. with which they compared them, is 

 wholly converted into oxalic acid, and does not yield an 

 atom of mucous acid, on being treated with the nitric acid, 

 if care be taken to separate all the mucilage that accompa- 



• Pickled onions, when long kept, perhaps tvo or three years, ac- 

 quire a saccharine taste, 50 as at length to lose almost all their acidity. G. 



nies 



