40 



On the Qrystalline Forms of Artificial Salts, [Ju i;y. 



- Bicarbonate of Potash. 



The primary form of this substance is a right oblique-angled 

 prism, which is not readily traced in the secondary crystals, but 

 may be derived from cleavage, and is shown 

 in fig. 1. There is also a cleavage parallel yig.i. 



to a plane passing through the diagonals 

 marked on tlie terminal planes. 



PonM, orT 90° 



M on the diagonal plane 53 

 MonT 103 



00' 



15 



25 



Fig. 2. 



The planes which appear on the crystals 

 are represented in fig. z ; but the planes e 

 are sometimes very disproportionately ex- 

 tended, so as nearly to efface T and/, giv- 

 ing to the crystals the character of another 

 primary form. 



The planes T do not commonly occur on 

 the crystals, and without these they nearly 

 resemble a secondary form of the right 

 rhombic prism ; they may, however, be dis- 

 tinguished by the unequal inchnation of M 

 on the two adjacent planes. On cleaving 

 or otherwise breaking the crystal, water 

 may be observed between the laminae, which probably occa- 

 sions the measurements on the cleavage planes not accurately 

 to agree. 



This is also the case with many other of the factitious salts. 



M on plane parallel to/ 127° 35' 



M on e 126 45 



T on e 156 50 



T on/ 128 50 



6 on/ 105 40 



Moiid Ill 00 



dond' 138 00 



Cyanuret of Mercuri/. 



I have received for examination from Mr. Cooper, of Lambeth, 

 6ome crystals obtained from oil of bitter almonds by digesting it 

 with red oxide of mercury. 



Mr. C. has also supplied me with some crystals of cyanuret of 

 mercury, procured in the ordinary way by boiling the red oxide 

 with Prussian blue. The crystals derived from both of these 

 sources correspond perfectly in their crystalline forms. 



I have not succeeded in cleaving them, but from their 

 measurements and modifications, a right square prism may be 

 regarded as the primary form. 



