1823.] 



Crystalline Forms of Artificial Salts, 



PonM, orM' 97° 



M on M' 88 



P on e, or e' 128 



Pon« 134 



Pon/i 100 



Pone' 122 



119 



10' 



30 



15 



50 



47 

 45 



Gallic Acid. 



Fig. 



These crystals, which were prepared by Mr. R. Phillips, and 

 are very minute, have one distinct cleavage parallel to the plane 

 P, and apparently another parallel to M. 

 The primary form is a doubly oblique prism, 

 and the measurements are as follows : 



P on M 95° 00' 



P on T . 125 20 



M on T 84 00 



Ton A- 160 00 



A;onM' 116 00 



P on 6 about 116 00 



b on M' about 150 00 



(6 is a very dull plane.) 



Oxalic Acid, 



The primary form is art obliqitt rhombic 

 prism. There are distinct cleavages parallel to 

 the planes M and M', but I have not observed m/ 

 any other. The crystals are usually attached 

 by one of the lateral ends of the figure, in 

 consequence of which the planes P, a, and 

 c, appear like lateral planes of a prism, and 

 M, M'', as its dihedral termination. 



Fig. 1 exhibits the common form of the 

 crystals ; and fig. 2 a modified form which 

 sometimes occurs, and not unfrequently with 

 only one of the planes e apparent at the late- 

 ral extremity, the other not being visible. 



P on M, or M' 98° 30' 



M on M' 63 5 



V ona 129 



Pone' 103 



P on e, or e' 107 



Fig. 2. 



20 

 15 

 00 



Citric Acid. 



Cleaves readily parallel to the planes M, M', and A, of the 

 annexed figure, but I can observe no cleavage in any other 

 direction. 



From the character of the secondary planes, the primary form 

 is a right rhombic prism, and the measurements taken chiefly 

 on a crystal I received from M. Teschemacher, are nearly those 



