18 B. J. Harrington — Nepheline, Sodalite, etc. 



The iron present was proved to be in the ferrous condition. 

 On decomposing the mineral with nitric acid of 1*20 specific 

 gravity, a residue was invariably left which did not consist of 

 undecomposed sodalite. At first it was supposed to be silica 

 which had separated from the sodalite, but on boiling with 

 strong solution of sodium carbonate only a small proportion of 

 it dissolved. This was included with the silica and the re- 

 mainder, which contained a few minute grains of magnetite 

 but which was not further investigated, was put down as 

 " insoluble." What is given as water is the result of a direct 

 determination, made by heating the powdered mineral in a 

 combustion tube in a current of dry air and collecting the 

 water in a chloride-of -calcium tube. A long piece of combus- 

 tion tube was employed, so that if any sodium chloride were 

 volatilized it would be condensed before reaching the chloride 

 of calcium. The end of the combustion tube next to the 

 latter was however found to be free from chlorides after the 

 operation. Heated in a platinum crucible for half an hour at 

 a low red heat, the mineral (after drying at 100° C), lost 0-34 

 per cent of its weight. With increased temperature the min- 

 eral continued to loss weight slowly, and after heating to 

 bright redness for about half an hour the total loss was 046 

 per cent. The sides and lid of the crucible were however 

 coated with a film of sodium chloride. Heated in a closed 

 tube the sodalite became perfectly white, while before the 

 blowpipe it fused easily, with intumescence to a colorless glass. 

 As stated above the sodalite is in places traversed by little 

 veins of a white and reddish mineral which proves upon 

 analysis to be orthoclase. It is mostly dull but in places shows 

 cleavage surfaces with a pearly luster. The reddish portions 

 probably owe their color to the decomposition of iron pyrites,, 

 occasional grains of which still remain. The specific gravity 

 at 18° C. was found to be 2*555 and analysis gave the follow- 

 ing percentage composition : 



Silica 63-00 



Alumina 18-93 



Ferric oxide - '59 



Lime - -08 



Magnesia '09 



Potash 12-08 



Soda 3-67 



Loss on io-nition 1 "00 



99-44 

 According to Dr. Adams the feldspar of the nepheline 

 syenite in which the sodalite occurs is entirely plagioclase, and 

 the occurrence of orthoclase as a secondary mineral in the 

 sodalite is of special interest. 



Chemical and Mineralogical Laboratory, McGill College, Montreal. 



