n PREFACE. 



acid was not actually obtained ; and this result, showing an excess in the 

 amount of the elements over that employed in the analyses, is due to the 

 caustic or subcaustic state of the ash. The error is in the carbonic acid, 

 and not in the essential elements. Carbonic acid is sometimes referred 

 to as if it were one of the original elements of the wood, while in reality it 

 usually results from the conversion in combustion of an organic into car- 

 bonic acid. So in the case of sulphuric acid, it is not oil of vitriol in grain 

 or straw ; but when burned, the sulphur of the proteine compounds acquires 

 oxygen, and hence it is often a secondary result. 



The irregularity in the numbering of the plates has arisen from the fact, 

 that when I began the volume, it was intended to embrace the descriptions 

 of the fruits ; but it was ascertained that the volume would be too large if 

 the original intention was carried out, and hence it was deemed advisable 

 to give the matter treating of the fruits in a separate volume. This part 

 of the work is considerably advanced, and will be ready for publication in 

 the course of the year. 



Albavt, February 1, 1849. 



