12 Prof. W. H. Miller on Graphitoidal Silicon and Boron. [Feb. 1, 



distinction being that the crystals of the latter are more perfect than those 

 of the former. 



Graphitoidal Boron. 

 The forms of boron have been described by the Commendatore Quintino 

 Sella in two papers read before the Royal jVcademy of Turin on the 4th of 

 January and the 14th of June, 1857, and by the Baron Sartorius v. Walters- 

 hausen in a paper presented to the Royal Society of Gottingen on the 1st. 

 of August of the same year. They found independently that the adaman- 

 tine boron of Wohler and Deville, containing a variable and not inconsider- 

 able amount of aluminium and carbon, considered by Sella as possibly a 

 definite compound of boron with aluminium and carbon with a mechanical 

 mixture of pure boron, crystallizes in forms belonging to the pyramidal 

 system. 



Boron containing 2*4 per cent, of carbon, the boro semplice of Sella, is 

 described by him as occurring in crystals, the faces of which are not so 

 perfect as to admit of a very accurate determination of the angles they 

 make with one another. The angles approximate to some of the angles of 

 crystals of the cubic system, but the aspect of the crystals, which are usually 

 twins, leads to the supposition that they belong to the oblique system, and 

 that the angle between the oblique axes differs but little from 99°. 



The forms observed by Sella, considered as belonging to the oblique 

 system, are : — 



A- 10 0, eOOl, c013, Wi0 2 3, 6 10 1, nlOA, phO^, ^20 3, /2 1, 

 Alio, r 2 1 0, 1 1 1, « T 1 2, 2 1 1, / 2 1 2. 

 Of these, I have since reobserved all, with the exception of a, d, I, and 

 perhaps p, the corresponding reflexion being too faint to enable me to 

 affirm the existence of that face in the crystals I examined. I have also 

 observed the following forms in which the distribution of the faces is in 

 most cases, probably in all, the same as in the prismatic system, or as if 

 the oblique form hkl were always^accompanied by the oblique form hkl; 

 m301, m; 104, v 403, 5:305, 5 2 2 3, ^ 3 3 2, z 221, 

 On the same supposition regarding the distribution of the faces, the an- 



