1864.] 



Dr. Phipson on Magnesium, 



317 



tion of pressure determines a proportionately imperfect and complicated 

 transformation of the gun-cotton upon its exposure to heat, the results of 

 which are more or less essentially of an intermediate character, so, con- 

 versely, the greater the pressure, beyond the normal limits, under which 

 gun-cotton is exploded — that is to say, the greater the pressure exerted by 

 it, or the resistance presented at the first instant of its ignition, the more 

 simple are the products of decomposition, and the greater are the physical 

 effects attending its explosion, because of the greater energy with which the 

 chemical change is effected. 



III. " On Magnesium.'' By Dr. T. L. Phipson, F.C.S. Communi- 

 cated by Prof. G. Gr. Stokes^ Sec. U.S. Received March 9; 

 1864. 



(Extract.) 



Iodine and Sidphur, — I find that iodine can be distilled off magnesium 

 without attacking the metal in the least. In the same manner I distilled 

 several portions of sulphur off magnesium without the metal being at all 

 attacked. 



Decomposition of Silicic Acid. — Heated for some time in a porcelain 

 crucible with excess of anhydrous silica, the metal burns vividly if the air 

 has access ; and a certain quantity of amorphous silicium is immediately 

 formed. Magnesium is therefore capable of reducing silicic acid at a high 

 temperature. The reason why potassium and sodium cannot effect this is 

 simply because these metals are highly volatile and fly off before the 

 crucible has attained the proper temperature. Magnesium being much less 

 volatile than the alkahne metals, takes oxygen from silica before volatilizing. 

 If the silicic acid be in excess, a silicate of magnesia is formed at the same 

 time ; if the metal is in excess, much siliciuret of magnesium is produced. 

 The presence of the latter is immediately detected by throwing a little of 

 the product into water acidulated with sulphuric acid, when the charac- 

 teristic phosphoric odour of siliciuretted hydrogen is at once perceived. 



Becommsition of Boracic Acid. — With boracic acid the phenomena are 

 rather different ; the acid melts and covers the metal, so that it does not 

 inflame even when the crucible is left uncovered. A certain quantity of 

 boron is soon liberated, and the product forms a greenish-black mass, which 

 oxidizes and becomes white in contact with water, and disengages no 

 odoriferous gas in acidulated water. 



Decomposition of Carbonic Acid. — I thought it would be interesting to 

 try a similar experiment with carbonic acid. Accordingly dry carbonate of 

 soda was heated with a little magnesium in a glass tube over a common 

 spirit-lamp ; and before the temperature had arrived at a red heat I observed 

 that carbon was liberated abundantly, and magnesia formed. 



Action of Alkalies. — A solution of caustic alkali or ammonia has little 

 or no action upon magnesium in the cold. 



