1819.] Dr. Clarke's Observations on Gehlenite. 451> 



were separated, and collected upon a second filter. The next 

 process related to the separation of the lime, which Gehlenite is 

 known to contain. To effect this, carbonateof ammonia was added 

 to the solution which had passed the filter ; and carbonate of 

 lime, being precipitated, was collected upon a third filter. The 

 solution now contained the muriates of ammonia and of the atkali 

 before mentioned. Being evaporated to dryness, a sufficient 

 degree of heat was communicated for the sublimation of the 

 muriate of ammonia, which came away in white fumes. Upon 

 adding a few drops of distilled water to the residue, and using 

 muriate of platinum as a test, a precipitate was caused by the 

 solution, and the presence of potass thereby fully demonstrated. 

 Upon adding also nitric acid to the alkaline solution, crystals of 

 nitrate of potass became visible. After this satisfactory experi- 

 ment, the remaining observations will be almost superfluous. 

 Indeed had I been earlier in possession of the information I 

 received from Dr. Wollaston, the method I pursued in the 

 analysis of gehlenite might have been rendered much simpler and 

 shorter. I will, however, state it with as much brevity as I can 

 from the notes which I then made. 



Gehlenite. 



External Characters. — Crystallized in oblique-angled parallele- 

 pipeds, nearly approaching to the cubic form. Crystals contain- 

 ing imbedded particles of carbonate of lime, appearing in white 

 specks ; exhibiting also ochreous surfaces as if in a state of inci- 

 pient decomposition ; set in all directions ; generally small ; 

 major diameter of the largest -^ths of an inch ; minor diameter, 

 T^ths; showing a tendency to cleavage on the solid angles. 

 Colour, greenish-grey ; lustre, resembling that of pitchstone. 

 Brittle, but hard when reduced to small fragments. Specific 

 gravity, in distilled water (temperature 59° of Fahr.), 2-71. 



Chemical Characters. — Colour, by trituration, dingy-white. 

 Before the blow-pipe fuses into a gumboge-yellow glass, which, 

 by continuance of the heat, becomes a dark cinder. Efferves- 

 cence in acids and gelatinization. Lime copiously precipitated 

 from the solution by oxalate of ammonia, and iron by tincture of 

 galls. 



Analysis. — One hundred grains, triturated in a porphyry mor- 

 tar, were placed in a covered platinum crucible, and exposed to 

 a smart red heat during half an hour. When taken out of the 

 crucible, a loss of weight was observed equal to six grains, owing 

 to the expulsion of water of absorption. 



A. To the remaining 94 gr. were added about four times their 

 weight of carbonate of soda, and the whole being placed in a 

 silver crucible was surrounded with sand in a second earthen- 

 ware crucible, and exposed to a red heat during an entire hour. 

 Being then removed from the furnace, and allowed to cool, the 

 cover was taken off, and distilled water added by degrees to soften 



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