1 823.] Crystalline Forms of Artificial Salts. 



m 



figures to each other will be readily perceived, and the less regu- 

 larly formed ones will, after a little practice in examii^ing tlifia, 

 be more easily understood. 



Chloride of Mercury. — Calomel, 

 1 have received from Mr. Coop(;r some good crystals of this 

 substance, which have afforded the measurements given below, 

 I have not found any distinct cleavage among these, but there 

 are indications of cleavages parallel to all the planes of a square 

 prism, which may be regarded as the primary form. The primary 

 form of the mineral, which has been called 

 muriate of mercury , is also a square prism, 

 and the secondary planes which replace the 

 terminal edges and angles of a crystal I have 

 measured, incUne at the same angles on the 

 lateral planes, as these do. 



Bichloride of Mercury, — Corrosive Suhlimg.t^, 



I am obliged to Mr. R. Howard for the crystals from which 

 this form has been determined. The cleavages arc parallel to 

 the lateral and to the terminal planes of 

 a right rhombic prism of 93° 44'. I have 

 not observed any modifications of the ter- 

 minal planes from which the dimensions of - 

 the primary form may be inferred. 



P on M, or M' 90° 



MonM'.. 93 



MonA 133 



00^ 

 8 



M 



■M 



M 



■\ 



A 



7^. 



Phosphate of Ammonia.* 



The primary form is an oblique rhombic 

 prism, and there are indistinct cleavages 

 parallel to the planes M and M'. The crys- 

 tals are usually lengthened in the direction 

 of the horizontal diagonal of the figure. 



P on M, or M' 105° 50' 



Ponc2 92 42 



Pone. 109 32 



M onM' , 84 15 



• For the crystals of this and the five following substances, I am obliged to Mr. 



Cooper, who informs me that he proposes to make collections of crystals of the artificial 



W; falts for sale ; aad h» contemplates tliat he shall be e^•bled to supply them at » \sxj 



moderate price. , 



