Kahlenberg—Action of Metallic Magnesium, Etc. 311 
water is chemically bound to the substance dissolved in it, the 
readiness with which metallic magnesium or sodium amalgam 
will liberate hydrogen from different solutions will in general 
be different. Again the difference of potential between mag¬ 
nesium and the solutions would be expected to be higher in 
the case of solutions that are vigorouslv attacked than in solu¬ 
tions in which the action is slight. The experimental data are 
in accord with this. If the chemical affinity existing between 
magnesium and the solution (regarded as a chemical combi¬ 
nation off solvent with solute) is sufficient to overcome the co¬ 
hesion of the magnesium, the latter is attacked; from the result¬ 
ing compound hydrogen splits off, and the rest m)a;y all remain 
as a homogeneous liquid (i. e.. all may remain dissolved) or 
further decomposition into a precipitate, the hydroxide or basic 
salt, and a solution may occur and usually does occur after the 
action has progressed for a, sufficient time. If no precipitate 
forms, the rate of change is not diminished by a decrease of 
the surface off metal exposed, and so the reaction is apparently 
aided. The more readily the dissolved products are removed 
from proximity off the surface of the metal by diffusion aided 
by mechanical stirring of some kind, the more rapidly the 
change progresses. Usually as the gas is rapidly evolved the 
liquid receives considerable stirring from this source. If the 
specific attraction called chemical affinity existing between mag¬ 
nesium and the solution, is not sufficient at the temperature 
of experiment, to overcome the cohesion of the mjagnesium, no 
action will take place, as in normal KOI! solution, for instance; 
if the affinity is barely able to overcome the cohesion, the ac¬ 
tion will go* on very slowly, as in the case off water. As stated 
above, magnesium amalgam does act on normal KOH solution 
with vigor, liberating hydrogen, forming magnesium hydrox¬ 
ide and setting mercury free. The explanation of the action 
is similar to the one just given. Here the affinity between the 
solution and the amalgam is sufficient to disintegrate the latter, 
and magnesium hydroxide forms in spite of the fact that it 
is difficultly soluble. Under the conditions off the experiment, 
it is evidently easier to abstract magnesium from magnesium 
amalgam than to overcome the cohesion off pure magnesium. 
