Count de Bournon on Bardigliom. 369 



When I thus determined the primitive crystal and integrant mole- 

 cule of bardiglione, the Tableau Comparatif des Result at s de la Crys- 

 tallographie et de P Analyse Chimique of M. I'Abbe Haiiy had not 

 appeared. This work informs me, that its learned author had also 

 determined the form of the primitive crystal, as well as of its inte- 

 grant molecule : and at the same time I perceive, with infinite regret, 

 that, as he was not more fortunate than myself with respect to the 

 height of these two molecules, the other dimensions he assigned them 

 differ from those to which I had been led by my study of this sub- 

 stance. According to this distinguished mineralogist, the base of th© 

 rectangular tetrahedral prism is not a square, but a rectangle, the 

 sides of which are to each other as 16 to 13.4 (fig. 5) ; the prism is 

 divisible in a direction parallel to its diagonals by planes, the inter- 

 section of which forms angles of 100° 6' and 79" 54' (fig. 6). Thus 

 It would be divisible Into rectangular rhomboidal prisms, the bases of 

 which would be rhombs of 100° 6' and 79° 54'. But these prisms, 

 it appears to me, cannot In any way be considered as the integrant 

 molecules of the tetrahedral prism with rectangular bases, considered 

 as the primitive one ; for this prism being also divisible in a direction 

 parallel to each of its sides, as shown at fig. 7, this second division 

 would separate each of the prisms with rhomboidal bases of 1 00° 6' 

 and 79° 54' into four rectangular trihedral prisms, of which two 

 opposite ones would have for their base an isosceles triangle of 

 100° 6', and the other two an isosceles triangle also of 79° 54', 

 fig. 5. Thus these molecules would be of two different forms, 

 and consequently could no more be considered as the Integrant mole- 

 cules of the substance, than those with rhomboidal bases of 100° 6- 

 and 79° 54'. 



On the other hand, this substance presents a very particular and 

 interesting fact, likely to mislead, with respect to the primitive 



3 A 



