132 Crystallography of the JSitrosoterpenes of Dr. Tilden. 



rays. The position of the acute bisectors was approximately 

 determined as being about 11^° on the normal to (1 0), and 

 321° on the normal to (1 1). 



II. Second group. — The second type of the crystals of nitroso- 

 terpene (figs. 4 & 5) includes those formed from the oils of 

 orange, bergamot, and caraway. They belong to the mono-sym- 

 metric system ; and their arc-elements may be represented as 

 10000 1 = 79°1', 1 1 1 = 38° 25f, 1001 1 0=40°25i'. 

 The crystals representing the orange and the bergamot pre- 

 parations, ^especially the former, generally give fairly good 

 images from the faces 01, 101, and 110; those from 

 100 are usually in the condition of many bands ; while the 

 reflections are never good from the face 101. The faces {0 01} 

 are generally hollowed. The reflections from the faces on the 

 caraway crystals, and particularly from 10 0. are less perfect 

 than those from the other preparations. In the following 

 Table the measurements marked with an S were made by Mr. 

 Elliot Steel. The only faces that occur on any of these crys- 

 tals are those of the following forms : — 



a, {100}; c, {001}; &,{101}; d,{101}; ^{110} 





Calculated. 



Bergamot. 



Orange. 



Caraway. 



ac 



ak 



cd 



da 1 



ad 



mm' 



mm' 



am 



mk 



m' d 



mc 



O / 



79 1 

 38 25| 

 24 4f 

 76 54f 



103 5^ 

 99 9 



80 51 

 40 25| 

 53 23| 

 99 56 



81 39| 



79 2||79S. 



1 

 79 



37 14 



24 4 & 24 6| 

 76 56 

 103 5 

 99 9 



t 

 79 



38 to 40° 

 24 8 

 77 21 



99 8 

 80 52 

 40 21 | 40°30'S. 



81° to 52° 



24 4 | 24° 6'S. 

 77 2 | 76 34 S. 

 103 3| 



99 7 | 99 10 S. 

 80 52 

 40 26% ] 40 25 S. 



81 41 



40 26-27' 



99 58 to 

 100 2 99° 50' 

 81 38 S. 



A distinct cleavage runs parallel to the faces of the form 

 001. It was not possible to determine the direction in the 

 crystal of the acute bisector of the optic axes. 



III. Terpene Hydrate (fig. 6). 



Crystals of terpene hydrate, made by Dr. Tilden from dextro- 

 and from laevo-rotatory turpentine-oil, exhibit no distinction 

 in the character of their forms. They are in fact crystallo- 

 graphically identical, belonging to the orthosymmetrical (or 

 rhombic) system, and presenting the forms a{10 0}, m{110}, 

 o{lll}, and £{101}, and occasionally b {0 1 0}. 



