Chemical Science. 1 65 



parts of acid, dissolves indigo without rendering it yellow, and 

 it may remain thus any length of time, without change. 



5. Robiquet on Volatile Oil of Bitter Almonds. — This, oil, 

 when exposed to the air for a few minutes, becomes a crystal- 

 line mass, and loses its odour. M. Vogel, who first remarked 

 the fact, found that the odour was restored by dissolving the 

 crystals in hydro-sulphuret of ammonia. He attributed the 

 loss of odour and change of state to oxidation, and the restora- 

 tion of odour by the hydro-sulphuret, as due to a deoxidation 

 effected by that substance. M. Robiquet, on the contrary, led 

 by his own particular views of aroma, (see Vol. x. p. 109,) 

 attributed the loss of odour to the loss of ammonia ; and its re- 

 storation, to the ammonia added in the hydro-sulphuret. 



With a view to illustrate the true cause of the phenomena, 

 M. Robiquet lately experimented on this subject. He found, 

 that instead of taking place in a few minutes, the crystalliza- 

 tion sometimes required several days ; and, in consequence, he 

 was led to distil the oil, collecting the results in different por- 

 tions. In this way he found, that the first portions underwent 

 no change in contact with the air, but that the last portions 

 crystallized immediately on exposure to it, or to oxygen, with 

 absorption of the gas ; whilst in nitrogen, hydrogen, carbonic 

 acid, or in the torricellian vacuum, no change took place. 



By further examination, it was ascertained that the most 

 volatile portion of the oil contained nitrogen, as an element ; 

 for when boiled with solution of potash, it gave prussiate of 

 potash, and when heated widi oxide of copper, nitrogen. The 

 less volatile and crystallizable parts contained no nitrogen; and 

 when pure and in crystals, it was found that the odour of bitter 

 almonds was not given to them by hydro-sulphuret of ammo- 

 nia. The crystalline matter appears to be an acid substance ; 

 it reddens litmus ; it is soluble in boiling water, and crystal- 

 lizes by cooling ; it is fusible, and readily volatile ; it unites to 

 alkalies, and appears to have no analogy with the oil fr»m 

 which it is derived. 



These two parts of the oil of bitter almonds, when examined 

 as to their action on the animal economy, were found entirely 

 different ; the more volatile was excessively poisonous, but the 

 crystallizable matter was quite inert. M. Robiquet, in con- 

 sidering the nature of the principle containing nitrogen, is in- 

 clined to consider it as different from prussic acid, though 



