39 2 



POPULAR SCIENCE MONTHLY. 



Molecular Depression 



of the Freezing Point 



the freezing-point, divided by 1.85, that should be expected if no dis- 

 sociation took place. As the figure shows, all the curves for the 

 non-conductors — in this case cane-sugar, propyl-alcohol and phenol 

 — converge towards unity with diminishing concentration. At higher 

 concentrations there occur deviations from the simple law. As ex- 

 amples of binary electrolytes are 

 chosen LiOH, NaCl and LiCl — 

 their curves all converge towards 

 the number 2. As ternary elec- 

 trolytes are chosen K 2 S0 4 , Xa 2 S0 4 , 

 MgCl 2 and SrCl 2 , they are decom- 

 posed into three ions, and their 

 curves therefore all converge to- 

 wards the number 3. 



As I had taken a step that 

 seemed most adventurous to chem- 

 ists, there remained to investigate 

 its chemical and physical conse- 

 quences. The most general and 

 wide-reaching of these is that the 

 properties of a highly attenuated 

 solution of an electrolyte ought 

 to be additive, that is, composed 

 of the properties of the different ions into which the electrolyte is 

 decomposed. This was already known to be the case in many in- 

 stances, and Valson had to this end tabulated his ' modules ' by the 

 addition of the one value for the negative to the other for the positive 

 ion, we may calculate the properties of any electrolyte composed of the 

 tabulated ions. In this way we may treat the specific weight (Valson), 

 the molecular conductivity (law of Kohlrausch), the internal friction 

 (Arrhenius), the capillarity (Valson), the compressibility (Rontgen 

 and Schneider), the refractive index (Gladstone), the natural rotation 

 of polarization (law of Oudemans), the magnetic rotation of polariza- 

 tion (Perkin and Jahn), the magnetization (Wiedemann), and all 

 other properties of the electrolytes hitherto sufficiently studied. 



The most important of these additive properties are those of which 

 we make use in chemical analysis. As is well known, it is generally 

 true that chlorides give a white precipitate with silver salts. It was 

 said formerly that silver salts are reagents for chlorine. Now we say 

 that silver ions are reagents for chlorine ions. This expression is 

 better than the old one, for neither all silver salts, e. g., potassium 

 silver cyanide and many other compounds of silver, nor all chlorine 

 compounds, e. g., potassium chlorate and many organic chlorides, give 

 this characteristic reaction. The experiment succeeds only with such 



Fig. 6. 



