CHAPTER XVII

BUNSEN, BERTHELOT, AND PASTEUR

Having traced the development of the science down to 1870, when the more fundamental of our modern views may be considered as definitely established, it seems appropriate to turn back and give an account of the work of three great chemists to whom little allusion has yet been made. They may all be considered as younger contemporaries of Liebig and Wöhler, but they entered far less than these men into. the theoretical controversies of their time.

The history of a nation should be a record of the development of the national character, but it is most easily written as a chronology of sieges and battles. So, too, the history of a science should record the progress of the race toward knowledge in some special field, but it easily becomes an account of dominant theories as they have superseded and conflicted with each other. Here and there, however, there arise great men whose life is not spent in the service of any theory, but who rather provide science with those facts to which all theories must conform.

Bunsen, Berthelot and Pasteur exemplify this. In spite of wide differences in temperament and in their fields of activity, they resembled each other in their aversion to all unessential hypothesis, in the fundamental value of their work to humanity, and in the energy and devotion which they gave to that service.

Bunsen.-Robert Wilhelm Bunsen was born in Göttingen, May 31, 1811, his father Christian Bunsen being the librarian of the University. After attending the gymnasium at Holzminden, he entered the university of Göttingen in 1828 and received the doctorate two years later, presenting a Latin thesis upon different types of hygrometers. Bunsen spent the winter of 1832-3 in Paris, and afterward traveled quite extensively, making longer stops in Berlin and Vienna. The year 1834 found him established as a docent in the University of Göttingen. In

1836 he succeeded Wöhler at Cassel, and three years later accepted a professorship at Marburg, which he retained till 1851. In that year he made a brief change to Breslau and then in 1852 accepted the professorship at Heidelberg which he retained till his retirement from active service in 1889. He died there August 16, 1899.

Cacodyl. As soon as Bunsen was settled at Cassel he began some investigations upon the organic compounds of arsenic which would alone have assured him recognition. Many years before, a French chemist named Cadet had distilled arsenious oxide with potassium acetate and obtained a liquid of a terrible odor which was not only intensely poisonous but also spontaneously inflammable. It is not surprising that these properties protected the substance from further investigation for many years. Bunsen, however, now attacked the problem, and found that the chief component of this dreadful liquid was an organic compound of arsenic, and that it had many of the properties of a metallic oxide. We now write the reaction which accounts for its formation as:

4CH3COOK + AS2O3 = 2CO2 +K2CO3 +

(CHAR)

As O
CH2

2

In Bunsen's time the determination of organic structure was not possible, but he recognized in the complex C4H12AS2 what was essentially a complex metal, to which he gave the name of cacodyl, Kd, on account of the terrific odor of most of its compounds. With acids the oxide formed salts:

Kdo + 2HCI = KdCl2 + H2O

the chloride, bromide, cyanide, etc., and when such a salt was treated with a metal like zinc, halogen was removed:

KdCl2 + Zn = ZnCl2 + Kd

and what in those days passed for the free radical was liberated. Of course we now know that the resulting compound, like dicyanogen, has twice the molecular weight of the true radical, but at the time this discovery was made, it was seized upon by Berzelius as one of the most important arguments ever furnished for the truth of the radical theory-ranking in this respect with

the cyanogen of Gay-Lussac and the benzoyl radical of Liebig and Wöhler.

In the successful investigation of these substances Bunsen established his reputation once for all as a master of chemical manipulation, but an explosion of cacodyl cyanide cost him the sight of his right eye, and weeks of illness resulted from inhaling its fumes. From this time on Bunsen devoted himself exclusively to work in the inorganic field.

Gas Analysis. About 1838 he undertook the investigation of blast-furnace gases, with the direct object of bringing about the most efficient use of the fuel. He accomplished this, but the study led to a revision and expansion of the whole subject of gas analysis, which proved classic, and Bunsen's one book Gasometrische Methoden is still a work of reference in this subject. More rapid methods have since been devised but none exceeded his in accuracy for many decades.

Geological Studies in Iceland.—In 1846 Bunsen spent three or four months in Iceland where he devoted himself to the study of the rocks, and took a great interest in the action of the geysers. Competent judges have referred to his work on the Icelandic rocks as laying the foundation of modern petrology, while his method of attacking the problem of geyser action seems of sufficient general interest to warrant a brief résumé here. Before this time most geologists had believed that the geyser water was volcanic. Bunsen, however, was able to prepare water like it in composition by boiling rain water with the local rocks, and came to the conclusion that it was really of surface origin. He also found that only the alkaline springs dissolved silica and only these formed geysers. A geyser according to Bunsen simply represents a deep tube or fissure in the earth in which alkaline water has settled and which is heated unequally by the hotter rocks around. In such a long narrow and nearly vertical tube there will be no free circulation of the water so that this will in general be considerably hotter toward the bottom than at the top. On the other hand, the pressure of the water column raises the boiling point of the water very markedly as the depth increases. By sinking self-registering thermometers at various depths into the tube, Bunsen found that a few minutes before the eruption the temperature at several places was very close to the