402 



NA TURE 



[February 3, 1910 



tiemenient diluees," which was published in the 

 '■ Bihang till Kongl. Vetenskapsakademiens Hand- 

 lingar,'' vol. viii., and was followed in the same year 

 by the second part, entitled "Thi^orie chimique des 

 Electrolytes." These researches contain the germ of 

 the theory of electrolytic dissociation, wdiich, however, 

 only received its complete statement in 1887, in the 

 first volume of the newly founded Zeitschrift jiir 

 physikalische Chemie. 



The impression made on the university authorities 

 by Arrhenius's thesis was not favourable. In their 

 view, apparently, it was neither very good chemistry 

 nor very good physics, and only deserved the mild 

 commendation "non sine laude approbatur." In- 

 deed, the fundamental conceptions of the new theory 

 were so much at variance with the current ideas of 

 both physicists and chemists that it can scarcely 

 excite wonder to find that a strenuous opposition 

 was offered to the introduction of the notion of free 

 ions into science. Had it not been for the warm 

 advocacv of Ostwald, who w'as already a power in 

 the dornain of physical chemistry, it is not at all 

 unlikely that the theory would have remained in 

 abeyance (as did Avogadro's hypothesis for nearly 

 fiftv years) until the necessity for it became impera- 

 tive. 



Happily, however, for the progress of science, the 

 appearance of the theory synchronised with that of 

 \an 't Hoff's theory of osmotic pressure, which it sup- 

 jjlemented by accounting for the apparent abnormali- 

 ties displayed by electrolytic solutions. Armed with 

 these two powerful weapons, Ostwald, by his writ- 

 ings, by his researches, and not least by his establish- 

 ment of a school of physical chemistry in Leipzig, 

 where, under his stimulus, the theories were prac- 

 tically applied by his pupils to the elucidation of 

 numerous problems in the physics and chemistry of 

 solutions, gradually overcame effective opposition, and 

 secured a permanent, if somewhat reluctant, recogni- 

 tion of the new ideas. To this period belongs the 

 fundamental application of the two theories by Nernst 

 to the calculation of electromotive forces. The only 

 parallel in physical chemistry to the activity and 

 fertility of those days is to be found in the contem- 

 porary development of radio-active research. 



We occasionally hear it said at the present time 

 tliat the theory of electrolytic dissociation is "played 

 out," that it was useful for a season, but that it must 

 now be superseded by something different and better. 

 Not many years ago, similar statements were made 

 regarding the kinetic theory of gases — that it had 

 served its purpose, was very good so far as it went, 

 and might be peacefully left to die a natural death. 

 To-day the kinetic theory is far from moribund, and 

 it seems to the present writer that a corresponding 

 vitality is inherent in the theory of Arrhenius. Wide- 

 reaching and fruitful physical theories generallv con- 

 tain a well-defined notion which survives any change 

 of form which the theory or its mechanical inter- 

 pretation may undergo. Dalton's atomic theorv con- 

 tains the imperishable notion of fixed combining 

 weights for the elements; Avogadro's theory contains 

 the definition of molecular weight ; and from these 

 two together W'e obtain, as Cannizzaro showed, the 

 modern atomic w-eight. Whether we believe in atoms 

 and molecules or not, these conceptions of combining, 

 atomic and molecular weights will persist unaltered, 

 and survive any upheaval in chemical theory. Simi- 

 larly, Arrhenius's great positive contribution to 

 physico-chemical science is the notion and practical 

 definition of degree of ionisation. Whatever be our 

 views of the origin and nature of ions, we must, in 

 any quantitative investigation of the properties of 

 XO. 2IOI, VOL. 82] 



electrolytic solutions, have recourse to the notion of 

 degree of ionisation. 



Arrhenius has since been active in many fields 

 besides that of physical chemistry, notably in cosmic 

 physics and in serum-therapy, bringing to bear in 

 these branches of science the same clear-headedness 

 and sublimated common-sense which enable him in 

 the multiplicity of the details he so easily masters 

 to detect the simple principles which coordinate and 

 govern the whole. The present volume, however, the 

 sixty-ninth of the journal which in its first volume 

 contained the statement of his theory, is only con- 

 cerned with his physico-chemical work, and is the 

 first of two volumes written in his honour by pupils 

 and friends to signalise the completion of the fiftieth 

 vear of his age and the twenty-fifth of his theory. 

 To it phvsical chemists in all parts of the world have 

 contributed, testifying to the universal esteem in 

 which Arrhenius and his work are held, and a fitting 

 introduction is written by Ostwald, who relates the 

 early historv and development of the theory with 

 many pleasant biographical and autobiographical 

 details. James Walker. 



PROF. F. W. KOHLRAUSCH. 



IT is with great regret that we have to record the 

 death of the eminent physicist, Prof. F. W. 

 Kohlrausch. 



Kohlrausch was born in October, 1840, at Rinteln 

 on the Weser. His father, Rudolph Kohlrausch 

 (1809-1858), was a physicist of great distinction who, 

 in conjunction with Wilhelm Weber, carried out for 

 the first time a determination of the ratio of the 

 electromagnetic to the electrostatic unit of electric 

 quantity, and thus laid one of the corner-stones of the 

 absolute system of electrical measurement. It was, 

 therefore, natural that the son's attention should be 

 early directed towards physical science. He studied 

 at Gottingen and Erlangen, graduated Ph.D. in 1863, 

 and in 1866 was appointed Professor Extraordinarius 

 at Gottingen. After about a year as professor of 

 physics at the School of Technology at Frankfort-on- 

 the-Main, he was appointed, in 1871, to a similar 

 post at the Grand-ducal Polytechnic at Darmstadt. In 

 1875 he became professor of physics in the University 

 of Wurzburg, and was transferred thence to Strassburg 

 in 1888. He was appointed president of the Phy- 

 sikalisch-Technische Reichsanstalt at Charlottenburg 

 in 1895, and, in the same year, was elected a 

 member of the .Academy of Science of Berlin and also 

 a Foreign Member of the Royal Society of London. 

 He was made honorary professor of physics in the 

 L'niversity of Berlin in 1900. He resigned his post 

 at Charlottenburg in 1905. He was elected an honor- 

 ary member of the Physical Society of London in 

 1906. He died at Marburg in January of this year. 



Kohlrausch was the author of a great number of 

 papers giving the results of experimental investiga- 

 tions in many branches of physics, but the subjects 

 which chiefly occupied him were the methods of mea- 

 suring magnetic and electrical quantities. Among 

 his contributions to this branch of science we may 

 mention his method for the absolute measurement of 

 the horizontal component of the earth's magnetic field 

 and of the strength of an electric current, by simul- 

 taneous observations of the deflection of the needle of 

 a tangent-galvanometer and of a suspended coil where 

 both instruments are traversed by the same current. 

 Another important set of experiments, published in 

 1874, had for its object the determination of the abso- 

 lute value of the " .Siemens unit " of electrical resist- 

 ance. The result which Kohlrausch arrived at, though 



