110 'Robiqnet on Aroma. 



which he named spiritus rector, Spon after his time, it was 

 found necessary to modify this idea, so as to allow various 

 kinds of spiritus rector, and Macquer divided them into acid, 

 alcaline, and oily. He admitted, nevertheless, that this odorous 

 effluvia was generally composed of an oil more or less dense, and 

 a subtile acid. At the time when chemical language was rege- 

 nerated, the expression of spiritus rector was changed for that 

 of Aroma. The existence of this fugacious principle once 

 admitted, it was necessary to assign it a situation in the sys- 

 tematic arrangement of bodies, and it was placed among the 

 proximate products of vegetables. The great difficulty was to 

 characterize it by properties belonging exclusively to it. It was 

 examined closely, and was soon observed to differ perpetually 

 from itself: its existence as a principle could not therefore 

 be supported, and Fourcroy first placed it amongst imaginary 

 bodies. This learned chemist, in endeavouring to overthrow the 

 opinions of Boerhaave and Macquer has perhaps departed still 

 farther from the truth. He regards all kinds of odours as 

 produced by the simple solution of the odorous substance in 

 the air, or in a fluid : thus, the essential oils and aromatics 

 owe their odour, according to Fourcroy, to a portion of them- 

 selves completely dissolved in the air, in water, or in alcohoK 

 This idea is not confined to the bodies hitherto considered 

 aromatic, but is extended to all substances ; and it is admitted 

 by the same author that each substance has its particular 

 odour, relative to its volatility and its solubility. It is also 

 admitted, as a consequence of this opinion, that the compounds 

 which contain a volatile principle, owe their particular odour 

 to it ; it was established, that the aroma of aromatic plants 

 resided solely in their essential oils ; and it resulted, that dis- 

 tilled waters owed all their smell to a portion of this oil retained 

 in complete solution in them. Such was the opinion supported 

 in the Memoir e, published in 1798, by Fourcroy, and the 

 experiments of Prevost and Venturi were advanced in support 

 of the results. 



Since that time no objection has been published : and this 

 view of tilings modified by the additional knowledge acquired on 



