VI 
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. 
Albany, February 1, 1849. 
