M 



1823. J Crystalline Forms of Artificial Salts. 45 1 



crystals I have seen is exhibited in fig. 3, Fig. 3. 



where the plane M' is so much less than M yf «r 

 as to confer on the crystal an appearance of 

 the base being rectangular, but not square ; 

 thus affording one of the numerous instances 

 which will be found among crystals, of de- 

 viation from regularity and symmetry in 

 their natural forms, by a disproportionate extension of some of 

 their planes, a character which would frequently lead to an 

 inaccurate determination of their forms, if the goniometer were 

 not resorted to. But the goniometer will generally correct the 

 erroneous conclusion derived from the appearance of the crys 

 tal ; as it has done in this instance, by showing that M on c, and 

 M' on c', measure alike, which it is highly improbable they 

 should do if the base of the prism were not square. 



Chlorate of Potash. 



The primary form is an oblique rhombic prism, some of the 

 crystals being modified as in fig. 4. The 

 cleavage is easy parallel to the planes M and Fig. 4. 



M', and the cleavage planes are brilliant, 

 but the only crystals I have are too thin to 

 obtain a cleavage plane parallel to P. The 

 measurements are as follows : 



PonM, orM'. .. 105° 30' 



M on M' 104 



Pone' 106 45 dull 



P on c, or e' 129 45 



Tartrate of Potash and Soda. — Rochelt 



The form derived from cleavage is a right 

 This is modified in the crystals measured, as 

 shown in fig. 5. 



t Salt. 

 rhombic prism. 



Fig. 5. 



P on M, or M' 

 P on c* 



• • • • 



90° 

 138 

 M on M' , 100 

 M on g 

 M' on </ 



} 



0' 

 50 

 



L63 



There is a peculiarity in all the crystals I 

 have seen of this substance which I do 

 not recollect to have observed in any others. 

 They are produced nearly in halves, and 

 appear to have rested or been formed on 

 planes which would have passed through the 

 middle of the entire crystal. One of these 

 is shown in fig. G. In 



Fig 6. 



natural segments 



• c is a dull plane, and occurs en only one of the crystals out of leveral that I have 

 seen. 



2c2 



