264 JUSTUS VON LIEBIG. 
An accidental occurrence drew A. von Humboldt’s attention to mein 
Paris, and theinterest which he took in me induced Gay-Lussac to com- 
plete in conjunction with me a piece of work which I had begun. 
In this manner I had the good fortune to enjoy the closest inter- 
course with the great natural philosopher; he worked with me as he 
had formerly worked with Thenard; and I can well say that the foun- 
dation of all my later work and of my whole course was laid in his lab- 
oratory in the arsenal. 
Ireturned to Germany, where, through the school of Berzelius, H. 
Rose, Mitscherlich, Magnus, and Wohler, a great revolution in inor- 
ganie chemistry had already commenced. Through the support of von 
Humboldt’s warm recommendation, an extraordinary professorship of 
chemistry at Giessen was conferred upon mein my twenty-first year. 
My career in Giessen commenced in May, 1824. Lalways recall with 
pleasure the twenty-eight years which I spent there; it was as if Prov- 
idence had led me to the little university. Ata larger university, or 
in a larger place, my energies would have been divided and dissipated, 
and it would have been much more difficult, and perhaps impossible, 
to reach the goal at which [Laimed, but at Giessen everything was con- 
centrated in work, and in this | took passionate pleasure. 
The need for an institution in which the students could be instructed 
in the art of chemistry, by which [ mean familiarity with chemical ana- 
lytical operations, and skill in the use of apparatus, was then being felt; 
and hence it happened that on the opening of my laboratory for teach- 
ing analytical chemistry and the methods of chemical research, students 
by degrees streamed to it from all sides. As the numbers increased I 
had the greatest difficulty with the practical teachings itself. In order 
to teach a large number at one time it was necessary to have a system- 
atic plan, or step by step method, which had first to be thought out 
and put to the proof. 
The manuals which several of my pupils have published later (I*res- 
enius and Will) contain essentially, with little deviation, the course 
which was followed at Giessen; it is now familiar in almost every labor- 
atory. 
The production of chemical preparations was an object to which I 
paid very particular attention; it is very much more important than is 
usually believed, and one can more frequently find men who can make 
very good analyses than such as are in a position to produce a pure 
preparation in the most judicious way. The formation of a preparation 
is an art, and at the same time a qualitative analysis, and there is no 
other way of making one’s self acquainted with the various chemical 
properties of a body than by first producing it out of the raw material 
and then converting it into its numerous compounds and so becoming 
acquainted with them. 
By ordinary analysis one does not learn by experience what an 
important means of separation crystallization is in skillful hands; and 
