278 INDEX I. 



And yet, with all this practical skill in decoction, 

 and accumulative industry in observation and 

 nomenclature, so far are our scientific men from 

 arriving, by any decoctive process of their own 

 knowledge, at general results useful to ordinary 

 human creatures, that when I wish now to separate, 

 for young scholars, in first massive arrangement 

 of vegetable productions, the Substances of Plants 

 from their Essences ; that is to say, the weigh- 

 able and measurable body of the plant from its 

 practically immeasurable, if not imponderable, 

 spirit, I find in my three volumes of close-printed 

 chemistry, no information whatever respecting the 

 quality of volatility in matter, except this one 

 sentence : — 



"The disposition of various substances to yield 

 vapour is very different: and the difference de- 

 pends doubtless on the relative power of cohesion 

 with which they are endowed."* 



Even in this not extremely pregnant, though 

 extremely cautious, sentence, two conditions of 

 matter are confused, no notice being taken of 

 the difference in manner of dissolution between a 

 vitally fragrant and a mortally putrid substance. 



It is still more curious that when I look for 



* ' Elements of Chemistry,' p. 44. By Edward Turner ; edited by 

 Justus Liebig and William Gregory. Taylor and Walton, 1840. 



