Dkcembee 30, 1898.] 



SCIENCE. 



931 



bringing ib to zero, whence the reaction 

 velocity gradually decreases and finally, 

 also, becomes zero. In the union of iodine 

 and hydrogen the increasing concentration 

 of the hydriodic acid formed, introduces a 

 gradually increasing opposing force, which 

 finally brings the reaction to rest. 



There is thus obtained a further princi- 

 ple, applicable in many directions. The 

 point at which a reaction comes to rest can 

 be calculated from the work of transforma- 

 tion. This was strikingly confirmed very 

 recently by Bredig and Kniipfifer, on the 

 basis of measurements of electromotive 

 force ; it was accurately determined when 

 the double decomposition of thallic chloride 

 and potassium sulphocyanate came to rest. 



But also the change in work of trans- 

 formation through changes in temperature, 

 pressure and mass can be calculated from 

 thermodynamics, and also the consequent 

 shifting of the point of equilibrium. Quan- 

 titatively expressed, this shifting always 

 takes place in the sense that cooling favors 

 whatever is formed with evolution of heat, 

 until finally, at absolute zero, all reactions 

 are completely displaced in this sense. Then 

 the course of the reaction would be con- 

 ditioned by the ' heat of transformation,' 

 which, at zero, would be equal to the work 

 of transformation. 



In studying equilibria from this stand- 

 point, not only the existence of every sub- 

 stance, but also the conditions of existence, are 

 determined. And it may be added, not 

 only the conditions of existence of indi- 

 vidual substances are determined, but also 

 all the compounds which it is possible to 

 obtain from given materials, say water and 

 salt. The reinvestigation of magnesium 

 chloride from this standpoint gave not less 

 than six different hydrates. 



This method of investigation closely re- 

 sembles the complete survey of a region 

 where formerly only individual cities and 

 villages were recorded. In the not very 



distant future inorganic chemistry may do 

 for geology what it has already done for 

 mineralogy in the preparation of individual 

 minerals. 



The views here expressed will be of chief 

 service in inorganic fields, since two ob- 

 stacles are in the way of applying them to 

 organic chemistry : First, the great pos- 

 sibility of compound formation. A single 

 pair of substances, as carbon and hydrogen, 

 gives rise to an unlimited series of com- 

 pounds. Second, the very sluggish man- 

 ner in which organic transformations take 

 place, causes reactions which are possible, to 

 proceed very slowly, or not to take place at 

 all. Thermodynamics stands here, in its 

 application, as before a very complex en- 

 gine which is rusted until it is useless. 



But the application of thermodynamics 

 to chemistry has been made in another di- 

 rection, and here the physical chemistry of 

 to-day has found its most fruitful field. 

 The possibility of determining the molecu- 

 lar weight of dissolved substances is given 

 by the so-called osmotic methods. A very 

 great need of inorganic chemistry would 

 thus be met. The molecular weights of 

 organic compounds, which are often volatile, 

 were generally known by determinations of 

 vapor-density. The inorganic compounds 

 investigated in this respect were, on the 

 other hand, exceptions. The work of a few 

 years has sufficed to fill up these omis- 

 sions. 



"We arrive, then, at our last point, a con- 

 sequence of these osmotic ■ methods, that 

 electrolytes — salts, acids and bases — are 

 broken down in aqueous solution in a pe- 

 culiar manner. The only explanation which 

 meets the case is that of Arrhenius, ac- 

 cording to which a dilute solution of, say 

 hydrochloric acid, would contain instead 

 of molecules of acid, negatively and posi- 

 tively charged atoms of chlorine and hy- 

 drogen. 



It is still impossible to pass final judg- 



