VOLATILITY OF MAGNESIUM. 263 



it a "difference-refractometer," and finds it available for obtain- 

 ing the strength of solutions, A solution containing '01 per 

 cent, of a given salt causes a deflection of '75 degrees, and a 

 solution containing 1 per cent, causes the shadow to recede 

 7"5 degrees ; a 2 per-cent. solution shows 15, &c. 



2,— NOTE ON THE VOLATILITY OF MAGNESIUM. 



By J, B. KIRKLAND, F.C.S., Assistant Lecturer and Demonstrator of 

 Chemistry, University of Melbourne. 



When the metal magnesium is heated to dull redness in a 

 glass vessel in an atmosphere of dry hydrogen, the glass in 

 contact with the magnesium becomes attacked, and covered 

 with a brown film of reduced silicon. So far this is what one 

 would expect from the powerful affinity of magnesium for 

 oxygen. But the glass, at a considerable distance from the 

 metal, also becomes covered with reduced silicon. The 

 explanation of this phenomenon is not plain, for at a dull red 

 heat the magnesium is not even fused, and we ordinarily 

 suppose it requires a high temperature to volatilise it. How, 

 then, can the glass be attacked at a distance ? One theory to 

 account for it was that the silicon just at the moment of its 

 reduction unites with the hydrogen to form silicon hydride, 

 and this being gaseous, volatilised, and decomposed in contact 

 with the hot surface of the glass, depositing silicon and 

 liberating hydrogen. This explanation did not meet the case, 

 for when the magnesium was placed in a clean iron boat, so 

 as to prevent contact with the glass, and heated, the latter 

 was still attacked immediately above the magnesium. 

 Another idea suggested itself — Has the hydrogen anything 

 to do with it? Experiments were made using carbon- 

 monoxide and sulphur dioxide, respectively, instead of 

 hydrogen, and curiously enough the glass wasnot attacked, 

 either in contact or away from the metal, but on raising the 

 temperature to the softening point of glass both these gases 

 were decomposed into their constituents, the magnesium 

 taking the oxygen. Another experiment was made, placing 

 the magnesium in a small iron boat, introduced into a tube 

 made of clean sheet iron, this being placed in a tube of hard 

 glass, and heated to dull redness in a current of dry hydrogen 

 for some time. The iron tube was examined after being 

 cooled, and the upper and distal end was covered with a 



