218 Prof. 'Ermm— Magnetic Elements at Berlin. [April 28, 



Precipitation of Metallic Solutions, — Magnesium precipitates nearly 

 all the metals from their neutral solutions. When these are taken in the 

 form of protosalts, even manganese, iron, and zinc are precipitated as black 

 powders. Aluminium and uranium (and perhaps chrome) are only pre- 

 cipitated as oxides. 



Alloys of Magnesium. — I have examined only a few alloys of magnesium. 

 Unlike zinc, magnesium will not unite with mercury at the ordinary tem- 

 perature of the air. With tin 85 parts, and magnesium 15 parts, I formed 

 a very curious alloy of a beautiful lavender- colour y very hard and brittle, 

 easily pulverized, and decomposing water with considerable rapidity at 

 ordinary temperatures. If the air has access during the formation of this 

 alloy, the mixture takes fire ; and if the crucible be then suddenly with- 

 drawn from the lamp, the flame disappears, but a vivid phosphorescence 

 ensues, and the unfused mass remains highly luminous for a considerable 

 time. A white powdery mass, containing stannic acid and magnesia, is the 

 result. 



[With platinum, according to Mr. Sonstadt, magnesium forms a fusible 

 alloy ; so that platinum crucibles can be easily perforated by heating mag- 

 nesium in them.] 



Sodium and potassium unite with magnesium, and form very malleable 

 alloys, which decompose water at the ordinary temperature. 



It is probable that an alloy of copper and magnesium, which I have not 

 yet obtained, would differ from brass, not only in lightness, but by de- 

 composing water at the ordinary temperature with more or less rapidity. 



Uses. — Magnesium will be found a useful metal whenever tenacity and 

 lightness are required and tarnish is of no consequence. The light fur- 

 nished by combustion of the wire has already been utilized in photography 

 at night. In the laboratory it will be found useful to effect decomposi- 

 tions which sodium and potassium cannot effect on account of their greater 

 volatility. 



April 28, 1864. 

 Dr. W. A. MILLER, Treas. & V.P., in the Chair. 



The following communications were read : — 

 I. On the Magnetic Elements and their Secular Variations at 

 Berlin/^ as observed by A. Erman. Commnnicated by General 

 Sabine, P.R.S. Received March 1, 1864. 



All observations and results to be mentioned here relate to 

 Latitude 52° 31' 55" North. 

 Longitude 13° 23' 20" E. from Greenwich. 



1 . Horizontal Intensity. 

 Denoting by (1800 + ^) the date of observation in tropical years of the 



