1823.] On the Crystallme Forms of Artificial Salts. 437 



Article IX. 



On the Crystalline Forms of Artificial Salts. 

 By H. J. Brooke, Esq. FRS. 



{Continued from p. 375.) 



Sulphate of Zinc, 



I A M indebted to Mr. Teschemacher for some brilliant and 

 remarkably perfect crystals of this salt, which may be cleaved 

 parallel to the plane h of the annexed figure, 

 but I have not observed distinct cleavages 

 in any other direction. 



The primary form is a right rhombic prism, 



MonM' 91° r 



Mon/ ]35 33 



M on A 134 27 



M one 128 58 



a on/ 120 



A one 119 23 



Sulphate of Nickel, 



I received some time since from Mr. R. Phillips some crystals 

 of this salt, which were right rhombic prisms ; and shortly after- 

 wards Mr. Cooper supplied me with others which were square 

 prisms. On noticing this difference of form, the first idea that 

 suggested itself was, that there might be some difference in the 

 proportion of water in the two salts, as both Mr. P. and Mr. C. 

 were satisfied, from the manner of preparing them, that both must 

 be free from impurity. The surfaces of the square prisms 

 obtained by Mr. Cooper not being so briUiant as might be 

 desired, he dissolved some of these crystals in distilled water, on 

 the evaporation of which he was surprised to find it deposit 

 rhombic prisms similar to those I had received from Mr. Phillips, 

 and without the intermixture of a single square prism. On 

 learning this fact, Mr. Phillips examined the solution from which 

 his first crystals had been obtained, and he found that it had 

 since deposited together others oi each of these forms, and the 

 crystals of each were observed frequently to inclose smaller ones 

 belonging to the other class. 



On these differences of form being discovered, Mr. Cooper 

 and Mr. Phillips analysed several quantities of the crystals of 

 each, and obtained nearly corresponding results, as will ap- 

 pear from a paper by Mr. PhiUips immediately following this. 

 Previously, however, to their analysis, Mr. Cooper reduced to 

 n?iinute fragments, and exposed to the air for several days, each 



