Physical C'hkmistuy and Vktki{inahy SciKNri:, 181 



beside the acid ranion (- SU^ - NO., - 01). Bases all contain the 

 negative monovalent liydroxylion (- OH) and a metal as kation 

 (K"*^ N"^ Ca"^"""). Salts are combinations of one of the various metals, 



as katiuns and an acid rest as anion (K"^' CI , t^ : SO ~, Ca"*"^ CO.-", 



' iSa^j ■» ' •' ' 



]\%"'""''-| far\^-)- The more a solution is diluted, the greater the number 



of electrolyt molectiles divided up in the ions, ionised or electrolytically 

 dissociated. 1 have already mentioned tliat the ions intluence the 

 freezing-point like molecules, the more extensive, therefore, the dis- 

 sociation the lower the freezing-point, the greater the difference be- 

 tween the calculated and the real depression, reduced to molecular 

 quantities. 



Hence the ilepression of the freezing-point of an electrolytic solu- 

 tion is a summarised expression of the effect of the undissociated 

 molecules plus the i(ms, and every ion has the same osmotic pressure 

 as every entire molecule. The depression of the freezing-point of an 

 electrolytic solution must be : — 



(1) An expression of the osmotic pressure. It is 22*34 atmo- 

 spheres if ^ = 1-85. For a, < or > than = 1*85, the osmotic pres- 



's, 



sure = 22-34: x , o-' 

 r8o 



(2) An e.xpression for the electrolytic dissociation. For instance, 

 if in an electrolytic solution of molecular concentration or respective 

 fractions of it, no dissociation would take place, the depression had to 

 be A = 1'85 ; as a matter of fact the depression observed ( A ) is more 



than 1-85 {A > 1'85) by dissociation, and therefore the quotient j:o~ 



is called coefficient of dissociation (Van 't Hoff). 



As the ions are carriers of electricity, the electrical conductivity 

 of a S(jlution must be better the more the molecules are dissociated, 

 and the conductivity being the reciprocit}" of the electrical resistance, 

 a measurement of this latter gives an indication of the relative number 

 of ions, and the degree of dissociation if the molecular concentration is 

 known. 



The methods of the electrical conductivity as an indication of the 

 active ions (and colloids) '■' or specific electrical resistance, and the 

 cryoscopical method t as an indication of the concentration of inole- 

 cules plus ions, are an. ply applied to the study of nearly every organic 

 liquid in human and veterinary medicine. I may mention the follow- 

 ing figures (p. 182) regarding the serum of normal animals (several 

 authors). 



About three-quarters of the salts in the different sera are electro- 

 lytes, and of these again nearly 75 per cent. NaCl, or about 50 per 

 cent, of the osmotically active substances consist of NaCl molecules 



' Apparatus generally used — Wlieatstone-Kirclihort'-Kolihausfh. 

 + Beckniauii apjiaratus vised. 



