236 Scientific InteUi(/ence, dfc. 



and the pyrites itself, were changed into peroxides, which, when 

 examined, were found to contain sulphate of lime, proving that sul- 

 phuric acid was formed during the action. 



The crystals of Traversalla are almost all rhomboidal. The colour 

 is grayish passing into brown. The mineral occurs in veins in the 

 mountains. To this form of crystals, Haiiy applied the terms 

 epigenous or false crystals. — Ulnstituty 80. 



XVI. — Metliod of detecting minute quantities of Sulphur. 



A SMALL bit of paper, coloured as if by sulphur having been wrapped 

 up in it, was submitted to M. Boutigny for examination. He 

 scraped off the yellow matter carefully, and triturating it in an 

 agate mortar with two grains of very pure nitrate of potash, pro- 

 jected it into an ignited porcelain capsule. Deflagration took place. 

 After cooling, the saline matter was dissolved in distilled water. 

 The solution was poured into a tube. A drop of a solution of 

 chlorine of barium was added, but no precipitation was produced 

 indicating the absence of sulphuric acid. To determine if this was 

 a correct method of proceeding, he repeated the experiment with 

 — i^th of a grain of sulphur, and he obtained a precipitate of sulphate 

 of* barytes insoluble in nitric acid. He collected it, mixed it with 

 soda, and submitted it to the action of the reducing flame upon char- 

 coal. The product of this operation was placed upon a moistened 

 plate of silver. Sulphuretted hydrogen was disengaged in a quantity 

 sufficient to be appreciable by the smell and to leave a black stain 

 on the silver. — Journ. de Chim. Med., i. 6. 



XVII. — Till discovered in Brittany. 



On the road from Rennes to Vannes, near the town of Roc St. Andre, 

 there are remains of excavations in a vein of white quartz. Tradition 

 states these to have been made for the use of a glass house, which at 

 one time existed here. M. Bellevue lately observed a brown substance 

 in this quartz, and sent specimens of it to M. Guilliton, at Blavier 

 and Lorieux. The latter found that the mineral was oxide of tin. 

 The purest specimens afforded 73 to 78 per cent, magnetic tin with 

 the -io^th of its weight of metallic iron. The brown specimens in 

 large crystals contain 19 per cent, of per-oxide of iron which may 

 be separated by muriatic acid. 



The quartz vein is about 30 feet wide, running in the direction of 

 N. 8' W., and possessing an inclination of 25° E. It passes through 

 granite which is fine grained, and contains much yellowish white or 

 reddish felspar. Greywackc occurs at no great distance from the 

 vein, along the canal from Nantes to Brest. The oxide of tin, which 

 occurs generally in well formed crystals, is only to be seen to a very 

 small extent. It is generally accompanied with mica, and frequently 

 also with arsenical iron, hematite, and emerald. At a short dis- 

 tance from the tin vein, to the E. and S. E., ferruginous sand stone, 

 rolled quartz, yellow flints, with sand and clay ai)pcar. — Ann. des 

 3Iines, vi. 381. 



