662 THE POPULAR SCIENCE MONTHLY. 



intrinsic truth, and the careful avoidance of all pretense in the 

 explanations ; it was the most complete contrast to the German 

 lectures, in which the whole scientific teaching had lost its solid 

 construction through the preponderance of the deductive method. 



An accidental occurrence drew A. von Humboldt's attention to 

 me in Paris, and the interest which he took in me induced Gay- 

 Lussac to complete, in conjunction with me, a piece of work which 

 I had begun. In this manner I had the good fortune to enjoy 

 the closest intercourse with the great natural philosopher; he 

 worked with me as he had formerly worked with Thenard ; and 

 I can well say that the foundation of all my later work and of 

 my whole course was laid in his laboratory in the arsenal. 



I returned to Germany, where through the school of Berzelius, 

 H. Rose, Mitscherlich, Magnus, and Wohler, a great revolution in 

 inorganic chemistry had already commenced. Through the sup- 

 port of von Humboldt's warm recommendation, an extraordinary 

 professorship of chemistry at Giessen was conferred upon me in 

 my twenty-first year. 



My career in Giessen commenced in May, 1824. I always recall 

 with pleasure the twenty-eight years which I spent there : it was 

 as if Providence had led me to the little university. At a larger 

 university or in a larger place my energies would have been di- 

 vided and dissipated, and it would have been much more difficult, 

 and perhaps impossible, to reach the goal at which I aimed ; but 

 at Giessen everything was concentrated in work, and in this I 

 took passionate pleasure. The need for an institution in which 

 the students could be instructed in the art of chemistry, by which 

 I mean familiarity with chemical analytical operations, and skill 

 in the use of apparatus, was then being felt ; and hence it hap- 

 pened that, on the opening of my laboratory for teaching ana- 

 lytical chemistry and the methods of chemical research, students 

 by degrees streamed to it from all sides. As the numbers in- 

 creased I had the greatest difiiculty with the practical teaching 

 itself. In order to teach a large number at one time it was neces- 

 sary to have a systematic 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 (Fresenius and Will) 

 contain essentially, with little deviation, the course which was 

 followed at Giessen ; it is now familiar in almost every labo- 

 ratory. 



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 



