T^$ An Attempt to arrange the 



I find to agree fo well with what I have obferved in nature, 

 that I am inclined to fuppofe Hauy's meaiures of the angles 

 are giv^n from calculation, affuming the cube as the nucleusy 

 and not from meafurement on the crj'ftal. De I'lfle's de- 

 fcription is as follows : 



" It is a blackifli kind of tin ore, in fmall folitary cryftals 

 five or fix lines in length, and at moft three in breadth. In 

 the variety in queftion, one of the extremities of the reftan- 

 gular tetraedral prifm firfl: prefents an oftaedral pyramid, the 

 planes of vi'hich forming with the prifm an angle of 155** 

 are irregular pentagons, having one of their angles of 60", 

 two of 120*', one of iio^, and the moft obtufe of 130"^ 

 Thefe pentagons form with each other angles of 110° and- 

 160°. The pyramidal form thence refulting is itfelf termi- 

 ,nated by a tetraedral fummit with trapezoidal planes join- 

 ing at right angles, as is obferved in the ifofceles triangles of 

 the third variety : but this fummit becomes oftaedral by the 

 flight truncature of its edges, from which refult four linear 

 hexagons that form by their contacl at the fummit of the 

 pyramid obtufe angles of 110^. The planes of the prifm, 

 had it not been broken, would be regular hexagons, and the 

 whole en, ftal would then have thirty-fix facets." De I'ljle'i 

 Cryjiallographie, Tom. IIT. p. 423. 



Having faid fo much refpefting the external form, a fe\V 

 remarks concerning the chemical analyfis of tin ores cannot 

 be mifplaced in a paper like the prefent. On this part of the 

 fubjeft, I cannot do better than by quoting from a paper of 

 C. Guyton, formerly and better known here by the name of 

 De Morveau, whofe chemical authority always carries great 

 Vveight with it. In his paper entitled, Obfervations on the 

 Acid of lin, and an Analyjis of its Ores, after giving the 

 analyfcs of the brown tin ore of Schlackenwald, as pub* 

 liihcd by Mr. Klaproth, which he verified himfelf, and 

 found to contain, tin 75, iron 0-5, filex 0*75, and oxygen 

 237,5 = 100; he proceeds to give a reafon why the tin cryf- 



taU 



