34 PHYSIOLOGICAL ROLE OF MINERAL NUTRIENTS. 



PHYSIOLOGICAL SUPERIORITY OF POTASSIUM SALTS. 



The question to what peculiar property of potassium its physio- 

 logical capacity must be ascribed implies also the questions: Why 

 can the physiological functions of potassium salts not be performed by 

 the related sodium salts? In reviewing- all the properties of the two 

 metals and of their compounds can not such chemical differences be 

 discovered as would also explain the great physiological difference? 

 Can there not be found in potassium chemical properties that give it 

 a certain superiority over sodium! 1 Long ago the writer searched for 

 striking and characteristic differences and believes he is justified in 

 calling attention to the following facts, which prove that potassium 

 and its oxid can brine on in certain cases a so-called chemical con- 

 densation which sodium and its oxid can not. For instance, carbonic 

 oxid can be condensed by potassium to triquinoyl, a benzene derivative, 

 but not by sodium (Lerch, Ntetzki). Phenol added to fusing potas- 

 sium hydroxid will, under condensation, yield diphenol among other 

 things, while with sodium hydroxid, oxidation, and but little condensa- 

 tion, is observed, resorcin and phloroglucin resulting (Barth). 



Among other noticeable differences may be mentioned, (1) that cer- 

 tain potassium salts condense ethyl aldehyde to aldol, while sodium 

 salts change it to croton aldehyde (Kopp and Michael); (*2) that potas- 

 sium acts on boiling triphenyl methane, resulting in the development 

 of hydrogen, but that sodium does not; (3) that potassium salicylate is 

 converted at 210 c C. into the isomeric paraoxvbenzoate," while in the 

 sodium paraoxvbenzoate just the reverse transformation is produced 

 at 300 c C. (Kolbe); (4) that potassium hydroxid decomposes peroxid 

 of hydrogen more quickly than does sodium hydroxid (Schone). 



It seems very probable to the writer that from the physiological point 

 of view the condensing properties of potassium are of prime impor- 

 tance. Substantial reasons exist for assuming chemical condensation 

 processes, not only in the formation of carbohydrates and fat, but also 

 in that of the proteins, i. e., in the three principal compounds of the 

 plant cell. The writer called attention to this probable role of potas- 

 sium salts in plants as early as 1880,^ and still holds this explanation 

 to be the correct one. 



It is very probable that for the condensing operations the organoids 

 of plant cells use a potassium-protein compound. It is well known, of 

 course, that chloroplasts require potassium salts for the assimilatory 

 function and further that they have an alkaline reaction.'' Final!}', 



a The corresponding rubidium salt in this case behaves similarly and therefore 

 bears more resemblance to the potassium than to the sodium salt. 



frPfluger's Arch., Vol. XXII, p. 510. 



cMolisch (Bot. Zeit., LS9S, No. 2) observed that as soon as the cells are killed and 

 the chloroplasts come in direct contact with the acid cell sap the cells of Coleus or 

 PerUla, rich in chloroplasts and containing anthocyan in an acid cell sap, underwent 

 the characteristic change from red to blue and green produced by alkaline sub- 

 stances. Cells of the same plants which are poor in chloroplasts <>r free from them 

 dp not show this change. 



