silver and chlorine compounds as are in a measurable degree decomposed into silver and chlorine ions. Ostwald has treated this question comprehensively, and in this way 
Fig. 7. he has given a rational exposition of the general phenomena of analytical chemistry. To this fact belong, also, the poisonous effect of some salts; this effect may be considered as a special physiologically chemical reaction of the chemical compounds. On this point there are many valuable researches by Krönig and Paul, Clarke and others.
A property that is of physical character, but is much used by the analytical chemist, is the color of the solutions. It has been subjected to a rigorous research by Ostwald. At first we will trace how a compound, e. g., fluoresceine, H12C20O5, behaves if one replaces its hydrogen atoms by other atoms, e. g., metals, iodine, bromine or atomic groups (NO2). The curves in the next figure (Fig. 7) indicate absorption bands in the spectra of the corresponding compounds. A replacement of K2 for H2 in the fluoresceine itself alters the absorption-spectrum in a most sensible manner. This depends upon the property that the fluoresceine is dissociated to a slight extent, which is in striking contrast
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| Fig. 8. | Fig. 9. | |
to the permanganic acid which will be discussed immediately. Instead of a single absorption-band in the blue in the first case, we find two absorption-bands in the blue-green and the green part of the spec-
