The well-known fact that the form of a specific substance, e.g. water, and hence its properties can alter without a change in composition was disposed of by the formal view that a physical, not a chemical, process was involved.

For, with pure water the inversion of cane sugar scarcely proceeds and subsequently it required very thorough, difficult studies before this effect and its order of magnitude were established.

In the first quarter of the nineteenth century the experimental proof for the interdependence of the composition and properties of chemical compounds resulted in the theory that they are mutually related, so that like composition governs like properties, and conversely.

The worst manifestations of exhaustion were successfully cured by a long period of rest but it was immediately apparent to me that I had lost once and for all my former capacity for carrying out experimental work until physically tired.

We know from biology that new forms of organisms simulate their primitive form as closely as possible at first, even though obliged to exist under changed internal and external conditions.

The development of a rational view of the nature of catalysis was thus absolutely dependent on the creation of the concept of the rate of chemical reaction.

My only supporter and comrade-in-arms was Georg Helm, who had endeavored to formulate an energetic conception of science before me and had presented his results in a treatise [Die Lehre von der Energie] exhibiting great independence of thought. But we were separated by his aversion to a realistic conception of energy. Consequently, each of us considered the other only a half ally, toward whom an attitude of caution was necessary.