ANALYSIS OF ONIONS." 201 



tial oil, which exists in it with a small quantity of acetous 

 acid. 



The part of the juice left in the retort deposited a fawn Examination 

 coloured matter, having a strong smell of* onions. From °| tlu> ) l,i .;'; lcft 

 pis seoiment alcohol .separated oil and sulphur. What was don. 

 not acted upon by the alcohol yielded by distillation a 

 black, fetid oil, and carbonate of ammonia, which indicate 

 the presence of a vcg-eto-animal matter, in the coagulum of 

 the onion juice. 



The fluid from which the preceding sediment was sepa- 

 rated had a deep brown red colour and a saccharine taste. 

 "With acetate of lead it gave a yellow precipitate. This 

 precipitate, heated before the blowpipe, grew black, emit- 

 ted a smeil of sulphurous acid, and left a globule of phos- 

 phate of lead. The solution of the residuum in sulphuric 

 acid diluted in water, heated, and filtered, yielded two pre- 

 ates of phosphate of lime on the successive addition of 

 ammonia and inne water. Hence the authors conclude, 

 that the precipitate formed by acetate of lead in distilled 

 onion juice is composed of oxide of lead, phosphoric acid, 

 sulphur, and a vegeto-animal matter. 



Messrs. Fourcroy and Vauquelin, having employed fer- Onion juice 



mentation as a ^ood mean of vegetable analysis on several exammL ' d b ) r 

 . . .,..'. . . . _ mean:; of fer- 



occasions Ttith success, tried it with onion juice. Exposed mentation. 



to a temperature of 15° or 20° [59° or 6b° F.] in a suitable 

 apparatus, this juice emitted no gas; but it acquired in 

 succession a tint of rose colour and of yellow, and a fawn 

 coloured sediment was deposited. The vessels being uu- 

 luted, they were surprised to find, that the juice was con- 

 verted into vinegar, but that it retained the onion smell as 

 strong as before fermentation. This proves, that the vola- 

 tile or essential oil had undergone no alteration. They 

 afterward found, that, if the alcoholic fermentation did not 

 take place, it must be ascribed to the absence of a suitable 

 ferment. 



The sediment formed during the acetous fermentation of Examination 

 the juice appealed to demand particular attention. This ol thi sediment 



i i i r i! • .• i, ■ • .'.. formed during 



substance has the ioi'owmg properties, n. it is in a state the acetifica- 



of minute division, forms a smooth paste, and has a strong tion of the 



onion smell, b. Alcohol takes up from it sulphur and oil, oniou i ulce ' 



U 2 as 



