Septembeb 6, 1907] 



SCIENCE 



301 



Kant to exclude chemistry from the list 

 of true sciences. In Kant's day, as he 

 rightly maintained, chemical inferences de- 

 pended so little upon any data capable of 

 mathematical treatment, that the experi- 

 menter was liable to fall into extraordinary 

 errors of interpretation. The world-wide 

 prevalence of the oddly inverted theory of 

 phlogiston, which imagined that a metal in 

 rusting lost something of its substance is 

 evidence of this defect. Such a theory be- 

 came untenable as soon as measuring, 

 weighing and the idea of number removed 

 the cause of Kant's reproach. 



Measurement, then, revolutionized chem- 

 istry—but what forms of measurement? 

 History tells no equivocal tale on this score ; 

 every form of measurement whose careful 

 application has laid the foundations of the 

 present science of chemistry is quickly 

 seen to belong to the domain of physics. 

 This is not surprising, since only two of 

 the traditional five human senses, namely, 

 taste and smell, are purely chemical in 

 their action ; and these are not easily 

 amenable to precise quantitative treat- 

 ment. All the other senses, sight, hearing 

 and touch, through which man obtains 

 knowledge of the outside world, depend 

 upon the interposition of physical energy ; 

 and the methods of measuring must cor- 

 respond to this fact. 



Thus, Joseph Black brought the balance, 

 an essentially physical instrument, into 

 requisition in order to demonstrate the 

 nature of the caustic alkalies. Lavoisier 

 used the balance to prove the fundamental 

 laws of conservation of mass. The same 

 instrument alone afforded Dalton a sound 

 basis for his laws of combining proportions 

 and of multiple proportions, and therefore 

 the first unimpeachable argument in favor 

 of the ancient atomic theory in which he 

 had believed from childhood. The study 

 of the densities of vapors, of the specific 



heats of solids, and of the forms of crystals, 

 all found by processes of physical meas- 

 urements, were the foundations upon which 

 by degrees a logical system of chemical 

 notation was built. The discovery of the 

 quantity-dimension of electrical energy led 

 in Faraday's hands to the new definition 

 of chemical equivalents. The spectroscope, 

 a physical instrument, in the hands of 

 Bunsen and Kirehhoff made possible the 

 detection of new chemical elements. Phys- 

 ical measurements of osmotic pressure led 

 van't Hoff to a new conception of the 

 phenomena of chemical relations in solu- 

 tion; and electrical conductivity was used 

 by Arrhenius as the basis of the generally 

 accepted theory concerning a large ma- 

 jority of the ordinary reactions between 

 inorganic substances. Both the free energy 

 change and the total energy change of a 

 system undergoing a chemical reaction are 

 measured by physical methods, and the 

 proof of Nernst's equation depicting the 

 mechanism of the galvanic cell depends 

 upon the precise evaluation of small elec- 

 tromotive forces. Again, Lord Rayleigh's 

 exact quantitative determinations of the 

 densities of gases with Ramsay's help led 

 to the discovery of a whole series of new 

 elements possessing extraordinary proper- 

 ties. Still more recently physical methods 

 of research are used in identifying the yet 

 more extraordinary radioactive substances, 

 and in endeavoring to solve the unanswered 

 riddle of their possibly transitory exist- 

 ence. Finally, exact analysis, based upon 

 weighing, alone made possible the exceed- 

 ingly complex syntheses of organic com- 

 pounds carried on by a long line of bril- 

 liant chemists culminating in Bmil Fischer. 

 These are only a few striking instances of 

 the discoveries in chemistry which are 

 essentially dependent upon physical proc- 

 esses. 



Thus if the various methods of measure- 



