132 



HEINRICn ROSE ON THE COMBINATIONS OF 



they are produced, and the larger and more regular they are. 

 By means of a very concentrated solution, we obtain them im- 

 mediately on coohng, but often very small, and therefore difficult 

 to be distinguished. 



The violent disengagement of carbonic acid gas ceases di- 

 rectly if the glass be closed, as the gas is absorbed by the liquid 

 through the pressure alone. 



The crystals of this salt, which were ex- 

 amined by my brother, have the form of the 

 annexed wood-cut. The planes d have, with- 

 out the planes a and c, the form of rhomboids, 

 therefore the planes dfg are the planes of 

 three rhombic prisms,' which render obtuse 

 the three edges of one and the same rhombic 

 octohedron ; the planes a b c ai-e the obtuse 

 planes of three angles of this rhombic octo- 

 hedron. 



The planes are in general very smooth and bright, and are well 

 adapted for accurate measurements, the plane c alone is generally 

 somewhat rounded. The crystals are perfectly cleavable, parallel 

 to the planes of the vertical prism ^ ; no other surfaces of cleavage 

 besides this were observed. The planes of the vertical prism are, 

 in the various deposits, sometimes large, sometimes small ; fre- 

 quently so small that the planes of the superior and inferior ex- 

 tremity are in contact. 



These crystals have undoubtedly been obtained before now ; 

 I produced them many years ago of considerable size, from 

 a solution of a great quantity of the sesquicarbonate, for which 



* Only the inclinations oi g to g-= 112° 9', and ^r to rf = 115° 6', are the 

 direct results of measurement ; the other angles mentioned are calculated from 

 those, but these also were measured, and the measured and calculated angles 

 were mostly found to differ only by a few minutes. 



