Kohlenberg—Action of Metallic Magnesium, Etc. 301 
upon, as were also solutions of ordinary and chrom alum. On 
the other hand the action was feeble on solutions of sodium 
phosphate, nitrate, thiosulphate, potassium ferrocyanide and 
the chlorides of barium, calcium and potassium. The work was 
entirely qualitative in charcter. Mouraour states that while 
LemJoine’s explanation of the action may hold good in the case 
of solutions of chloride of magnesium, for instance, for most 
of the salts last; mentioned it is inadequate. In the case 
of the ammonium salts Mouraour ascribes the action to the 
fact that solutions of these salts dissolve magnesium hydroxide. 
But he states that in the case of the salts of Pb, Cu, Hg, Co, 
from which magnesium precipitates the heavy metals and simul¬ 
taneously liberates hydrogen, we have a secondary action of the 
magnesium! on the water of the solution. He deems it very dif¬ 
ficult to explain the phenomena, in the cases last mentioned, 
stating that it is not probable that salts of these heavy metals 
favor the solubility of magnesia. Mouraour was apparently 
not aware of the work of Tommasi. As a matter of fact mag¬ 
nesium hydroxide is not formed at all when solutions of the 
heavy metals named are acted upon by magnesium; the salt 
of the latter metal forms and remains dissolved, the basic salt 
or hydroxide of the heavy metal being precipitated. In fact, 
the cases which Mouraour finds difficult to explain are really 
most readily explained; for the salts of the heavy metals are 
indeed slightly decomposed by water, a small quantity of free 
acid being liberated as the acid reaction of such solutions clearly 
shows. This acid acts on the magnesium evolving hydrogen 
and forming the corresponding magnesium salt, a basic salt or 
hydroxide of the heavy metal resulting simultanously. 
In presenting to my students the various ideas that have from 
time to tim/e been entertained by scientific men regarding the 
nature of solutions, I have always laid considerable stress upon 
the view that the process of solution depends upon a mutual in¬ 
teraction of solvent and solute, and that solutions are chem¬ 
ical combinations 1 of solvent and solute according to variable 
1 ‘Compare Mendelejew, Principles of Chemistrj'-, Vol. I; Pickering, on 
Solutions, Watts Chemical Dictionary; Horstmann, Graham-Otto, Lehr- 
buch der Physikalischen und Theoretischen Chemie, Yol II. 
