1866. | Hofmann and Modern Chemistry. 63 
Chemistry was making valuable discoveries in the mineral world, it 
had done but little toward elucidating any of the phenomena of the 
vegetable and animal kingdoms. Priestly had, it is true, discovered 
the influence of growing plants upon the air, and of light upon the 
growing plant.* Dr. Ingenhousz had observed the peculiar nature 
of the air “ produced by a special operation carried on in a lving 
leaf.” And Sennebier found that plants yielded more “ dephlo- 
gisticated air” (oxygen) in distilled water impregnated with “ fiaed 
air” (carbonic acid) than in simple distilled water. 
All these men were floating round and gradually approaching 
the truth. Cavendish proclaimed that “fixed air is a principal con- 
stituent part of vegetable substances,” but even he was bewildered 
by the Phlogistic Hypothesis, and it was not until Lavoisier 
destroyed it that any real advance was made. 
Davy stands forth amidst the philesophers of his day as a re- 
markable discoverer. ‘The brilliancy of his experiments, which 
proved the metallic nature of the earths and alkalies, and the 
elegance of those investigations which determined the true cha- 
racter of muriatic acid, has led his ‘ Agricultural Chemistry’ to be 
almost forgotten. In this book, however, will be found the first 
clear exposition of the part which chemical forces play in all the 
processes of the living organisms, and an examination of the trans- 
formations and changes in plants and animals which are dependent 
on their influences. After Davy for a long period but small 
advance was made, and it is not a little curious to find Liebig in 
1841 writing as follows :— 
“Since the time of the immortal author of the ‘ Agricultural 
Chemistry,’ no chemist has occupied himself in studying the appli- 
cation of chemical principles to the growth of vegetables, and to 
organic processes. I have endeavoured to follow the path marked 
out by Sir Humphry Davy, who based his conclusions only on that 
which was capable of inquiry and proof. This is the path of true 
pluilosophical inquiry, which promises to lead us to truth, the proper 
object of our research”. 
It is not strictly true to say that Organic Chemistry had no 
existence between the time of Priestly and of Liebig. We find 
many chemists, as Pelletier, Vauquelin, Chevreul, Fourcroy, and 
others carefully examining the proximate principles of plants, and 
Berzelius gave the world his ‘ Animal Chemistry’ within this period. 
But it must be conceded that until the Professor of Chemistry at 
Giessen taught Chemistry in its relations to organization and life, 
the study of Organic Chemistry lagged in the back-ground. , 
* «Experiments and Observations relating to various Branches of Natural 
Philosophy, with a Continuation of the Observation on Air.’ By Joseph Priestly, 
LL.D., F.R.S. Birmingham, 1781. 
_t ‘Chemistry in its Application to Agriculture and Physiology.’ By Justus 
Liebig, M.D., F.R.S., &e. 1842. 
