362 Oil the Houghite of Prof. Shepard. 



pearance, bat were more or less opake white externally and with- 

 out exception were pervaded by minute grains of spinel and 

 phlogopite. Some of them presented a portion just within the 

 opake layer, that was transparent and homogeneous : within this, 

 fragments and crystals of spinel predominated. These statements 

 are necessary as a preface to the account of my chemical inves- 

 tigations, after detailing which, the physical properties will be 

 again referred to. 



The mineral subjected to analysis, comprised fragments par^ 

 tially opake and partially translucent, as it Avas almost impossible 

 to procure by separation a homogeneous material. After igni- 

 tion, it manifests an alkaline reaction, and this, as I have since 

 found, it also does before heating. 



As stated by Prof Shepard, it is decomposable in acids, before 

 and after ignition. A large nodnle, slowly dissolves, even in cold 

 acetic acid. Carbonic acid is evolved daring solation, and in 

 sufficient quantity to produce a precipitate on passing through 

 baryta water. A residue has always occurred in my experiments, 

 consisting in part of insoluble minerals, — spinel and phlogopite, 

 and also in most cases of silica; and in fact, the mineral has 

 often afforded a well characterized jelly with acids. The acid 

 solution gives with ammonia, in presence of chlorid of ammo- 

 nium, a copious white precipitate. The filtrate contains only 

 magnesia, or occasionally a trace of potash, possibly from decom- 

 position of phlogopite. The ammonia precipitate, as noticed by 

 Prof Shepard, yields alumina and a trace of iron to caustic pot- 

 ash, but is not entirely decomposed even by a large excess of it, 

 daring protracted digestion at a boiling heat. Following the 

 usual routine of analysis it was repeatedly, and most carefully 

 examined for all the salts and rare earths that can occur in such 

 circumstances, but no evidence of their existence was obtained. 

 It appeared to be a hydrous compound of magnesia and alumina, 

 and upon reference to Gmelin's Handbuch, notice of such a sub- 

 stance was found. By three or four repeated solutions in hydro- 

 chloric acid, and precipitations by ammonia, it was completely 

 separated into the two earths, alumina and magnesia; which 

 with water completed the sura of its ingredients. 



Previous to entering on the quantitative investigation of this 

 mineral, I made inquiries of Dr. Hough, who resides near the lo- 

 cality, hoping to obtain homogeneous specimens. He could not 

 furnish them, and the following analyses were made without ex- 

 pectation of perfectly accordant results. 



In the analysis, carbonic acid was determined, in the usual man- 

 ner, in a flask furnished with chlorid of calcium and aspirating 

 tubes. Water was expelled by ignition, and collected in chlorid 

 of calcium. The mineral was decomposed in hot hydrochloric 

 acid, the whole evaporated to dryness, redissolved, and filtered; 



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