512 



Dr. L. Vegard on 



Anatase (Ti0 2 )- 



§ 5. This mineral is isomeric with rutile, but although both 

 crystals belong to the ditetragonal bipyramidal class of the 

 tetragonal system they are not isomorphous. For rutile 

 the ratio c:a is equal to 0*644, for anatase it is equal to 

 1-777. 



Also, in the case of anatase, we had some difficulty in 

 obtaining reflexion from a sufficient number of faces ; but 

 finally we succeeded in finding a number of maxima for the 

 following five : (100), (001), (110), (111), and (112). 



The positions and intensities of the observed maxima are 

 given in Table III. and in fig. 3. 



Table III. 



n. 



(001). 



(100). 



(110). 



(111). 



(112). 



9. 



I. 



9. 



I. 



9. 



I. 



9. 



I. 



9. 



I. 

 1-5 



1 



7° 30' 



10 



13° 19' 



5-8 



9° 21' 



32 



5° 0' 



4-6 



11° 48' 



2 



15 8 



0-6 



27 26 



1-4 



18 58 



08 



10 2 













3 



23 3 



0-15 





... 







15 9 



0-3 







4 



32 50 



0*14 











20 24 



0-5 







If we would write the formula (Ti0 2 ) 2 as in the case of 

 rutile, we should find that only ^\ of a molecule is associated 

 with the elementary cell d 100 2 d Q 1} or just half the number 

 found for the rutile cell. 



For the ratios of the spacings we get : 



dioo : d m : d m : d m : d m = l :1'418 : 2'643 : 1-765 : 1-126, 



or approximately 



-4c 1 



= 1: V2: 



V'+crvc-) 



*+i 



These are exactly the ratios which correspond to a lattice 

 of the diamond type which is drawn out in the direction of 

 the tetragonal axis. For the sake of comparison we 

 remember that in the case of the isomeric substance, rutile, 

 the lattice of the Ti atoms is composed of two lattices of the 

 diamond type put inside one another in such a way that 

 the elementary cell is not altered. The lattices give the 



