1896 | TOXIC ACTION OF DISSOLVED SALTS 83. 
solution or the lowering of the freezing point of the same, were 
explained from theoretical standpoints by the above mentioned 
work of van’t Hoff, and so these methods were placed upon a 
thoroughly scientific basis. Solutions that showed too great an 
osmotic pressure also showed too great a diminution of the vapor 
tension or too great a lowering of the freezing point, and conse- 
quently too small a molecular weight. 
In his mathematical formule van’t Hoff for the time being 
arbitrarily introduced a factor 7 to account for the deviations 
that such solutions showed from what the theory required. 
Soon, however, Arrhenius,’ from the relation between the lowcr- 
ing of the freezing point of solutions and their electrical conduc- 
tivity, came to the conclusion that in aqueous solutions of salts, 
acids and _ bases, in short, in solutions that are conductors of 
electricity, the dissolved substances showing too small molecular 
weights (as did the chloride of ammonium in the vapor state) 
are to be regarded as being dissociated® into part-molecules or 
ions.? These ions are charged with electricity, each gram-equiva- 
lent bearing 96,540 coulombs. This latter figure has been deter- 
mined by experiments on electrolysis and has well been termed 
the constant of Faraday’s law. There are ina solution of an 
electrolyte as many ions charged with positive electricity as with 
negative electricity and thus the electrical neutrality of the solu- 
tion is preserved. 
Viewing things, then, in the light of the theory of Arrhenius, 
we have, for example, in a solution of sodium chloride sodium 
tons and chlorine ions, besides a certain number of undissociated. 
sodium chloride molecules. Experiments on the electrical conduc- 
tivity show that in this case dissociation is practically complete 
when one gram-molecule (7. ¢., 23+35.5=58.5 grams) of the salt 
is dissolved in 1000 liters of water. There are at this dilution then 
, solution not NaC] molecules, but Na ions and Clions. These 
are usually written Na- and Cl, 
5 Zeitschr. f, physik. Chem. 1:631. 188 
. i j ; 4 * . : 
el Because this dissociation takes place only in case of electrolysis it is termed. 
oe issociation, ‘ 
A term that dates back to Faraday. 
