Mr. Teschemacher on the Crystalline Form of some Salts, 27 



was invisible,- I never lost sight of it, till I saw both it and the 

 smaller one quite clear of the moon. 



But the larger one was so nearly occulted here, that it must 

 have been quite so at a very small distance to the north-east- 

 ward ; and it would be curious, and not quite useless as con- 

 nected with the question of lunar parallax, if it should be 

 found that the occultation was observed where the star's ap- 

 parent path was an accurate tangent to the moon's limb. 

 I am, Gentlemen, yours, &c. 



Greenwich Hospital, Dec. 10, 1827. E. RlDDLE. 



VI. On the Crystalline Form of some Salts. By Mr. 

 E. F. Teschemacher. 



To the Editors of the Philosophical Magazine and Annals. 



Gentlemen, 



{OBSERVING a paper in your Journal of December last, 

 ^^ on some new double chromates, I beg to remark, that 

 during an investigation which I made last winter, of some of 

 the combinations of chromic acid with the different metals, I 

 met with the same salts ; and by an examination of their cry- 

 stallographical character arrived at the same results as Mr. 

 Henry Stokes, with regard to the combinations of sulphate 

 of nickel and sulphate of zinc with chromate of potash, which, 

 as they have not been before described, it may be interesting 

 to detail. 



Struck with the similarity in form of the crystals deposited 

 by the solution containing nickel with some crystals of sul- 

 phate of nickel and potash given to me by Mr. H. J. Brooke, 

 and described by him in the Annals of Philosophy, New Series, 

 for December 1823; I subjected some very brilliant crystals 

 of this new salt to an examination by Dr. Wollaston's reflec- 

 tive goniometer, which gave the following measurements. 

 — Primitive form an oblique rhombic prism. 



Chromo-sulphate of Nickel 

 and Potash. 



P on M or M' 101° 37' 

 P on e ... 154 30 

 M on M' . . 107 37 



A small difference in the meeting of the angles of these two salts 



E 2 will 



