1823.] Crystalline Forms of Artificial Salts* 375 



figure, analogous to some which have been before noticed; 

 there being on some of the crystals only one of the planes b 

 replacing each of the solid angles on which two are placed in 

 the drawing, and these being the alternate 

 planes. Many of the crystals present, 

 however, the pairs of planes 6, as shown in 

 the figure. 



PonM,orM^ 90° 



P on c, or c' 143 



cone' 107 



i; on // 126 



MonM' 104 



M on/ 142 



M on A 127 



Uonh 121 



M'on.6 97 



0' 

 30 





 30 



6 



3 

 57 





 21 



have 

 form is an 



Carbonate of Magnesia. 

 The crystals from which this figure has been given, I 

 received from M. Teschemacher. The primary 

 oblique rhombic prism ^ which maybe cleaved, 

 but not distinctly in the small crystals I 

 have attempted to operate upon, parallel to 

 the planes M and M^ 



PonM,orM' 102° 0' 



P on e, or e' 120 30 



M on M' 86 30 



M on A 133 15 



Monk 13G 45 



Sulphate of Cinchonia, 



Mr. Pope, of Oxford-street, has favoured me with some minute 

 crystals of this salt : from which the primary form appears to be 

 a doubly oblique prism, having cleavages parallel to all its planes. 

 The cleavage, however, parallel to P is not very distinct. Some 

 of the crystals are of the form I have given, but there are others 

 whose figure does not appear to be imme- 

 diately related to it. These are probably 

 hemitrope, or rather quadruple crystals, 

 united by secondary planes ; but they are 

 not sufficiently distinct in character to ena- 

 ble me at present to trace their precise rela- 

 tions to the primary form. 



P on M 95° 50' 



P on T 90 



M on T . , . . , 83 30 



M 



