98 Historical Sketch of Improvements in [Aug. 



of a peculiar nature. Its colour is white or bluish-white, its 

 fracture foliated, and the shape of the crystal is described as 

 sometimes the same with that of felspar, and sometimes a six- 

 sided prism (two figures scarcely compatible with each other). 

 Its hardness is equal to that of felspar, and it is infusible per se. 

 Had the specific gravity and the chemical composition of the 

 mineral been stated, it would have enabled us to judge with 

 greater accuracy whether the necronite be not a variety of some 

 mineral already known. Were it not for the shape of its crys- 

 tals, I should be disposed to consider it as a variety of spinell. 

 (See Ainiah of Fhitomphy, xiv. 68.) 



3. Carbonate of Magnesia. — This mineral in the state of fine 

 acicular crystals has been discovered by Mr. James Peirce con- 

 stituting veins in a serpentine rock at Hoboken, in Staten Island, 

 on the New Jersey side of the Hudson. (Ibid. p. 69.) 



4. Zircon. — I have mentioned in the Annals of Philosophy, 

 xiv. 147, that this mineral is not a simple combination of silica 

 and zirconia, as has been hitherto supposed, but that it contains 

 likewise a quantity of alumina. 



6. Gehlenite. — In consequence of Dr. Clarke's discovery of 

 potash in this mineral, I subjected it to two different analyses 

 without being able to extract any of that alkali. I consider 

 myself, therefore, entitled to affirm, that the quantity of alkali 

 which gehlenite contains, if any, must be extremely small. 



During my experiments on gehlenite, a phenomenon occurred, 

 which (though I might have anticipated it) occasioned me some 

 trouble at first. The gehlenite reduced to a fine powder was 

 fused with four times its Aveight of nitrate of barytes. After 

 softening with water, the whole was dissolved in muriatic acid, 

 and the barytes thrown down by means of sulphuric acid. 

 After separating the sulphate of barytes, the whole of tlie earthy 

 bodies in the solution were precipitated by means of carbonate of 

 auinionia. The liquid after filtration was evaporated to dryness, 

 and tlie dry residue was exposed to a red heat in a platinum 

 crucible. A saline substance remained, which deliquesced on 

 exposure to the air, and possessed the taste and all the charac- 

 ters of muriate of lime. I obtained the same residual salt in two 

 diit'erent experiments before I turned my attention to the circum- 

 stance. The cause of this residue I suppose to be that a little of 

 the lime is kept in solution by means of the excess of carbonic 

 acid (for the carbonate of ammonia of commerce is always a 

 sesquicarbonate at least). This portion at a red heat decom- 

 poses a portion of the sal-ammoniac, and forms muriate of lime. 

 1 find the existence of this residual salt to be uniibrm whenever 

 muriate of lime is precipitated by the carbonate of ammonia of 

 commerce. 



6. Kgcran. — This mineral, considered as a variety ofidocrase, 

 has been analyzed by Count Dunin Borkowski, and found to be 

 composed as follows : 



