430 M. Stromeyer on Polyhalite. [Dec. 



ments are perfectly transparent, the larger ones only at the 

 edges ; but if separated into very thin scales, and held up 

 against the light, it is transparent, and nearly colourless. 



When scratched, it exhibits a reddish white streak. 



It has neither any smell of itself, nor emits any when either 

 rubbed or breathed upon. 



Fragments of it do not shine in the dark, when rubbed toge- 

 ther, or scraped with the point of a knife, neither does the dust 

 produce any phosphoric light when thrown on red-hot coals. 



It is not possessed of any electric properties. 



It is not at all affected by the magnet, neither does the 

 latter attract particles of its finest dust. 



It attracts a little moisture from the atmosphere. 



Chemical Analysis of Polyhalite. 



1. Preliviinary Analysis of Polyhalite. — Having already 

 made a few remarks respecting the physical characters of 

 polyhalite, we now come to a chemical analysis of it, and to 

 various introductory experiments made for the purpose of obtain- 

 ing a knowledge of this mineral, and of the nature of its consti- 

 tuent parts. 



(A.) Examinatian of Polyhalite by Heat. 



a. A piece of polyhalite held in a platinum spoon over the 

 flame of a spirit lamp soon loses its transparency, and gradually 

 turning white assumes a reddish-white appearance, its cohe- 

 rence likewise is diminished, and although its particles are 

 rendered harder by calcination, they adhere less to each other. 

 When the flame is increased so as to render the spoon red-hot, 

 the fossil melts, and is coiiverted into an opaque brown mass. 



b. It undergoes a similar change whenever a piece is held in 

 a pair of forceps in the flame of spirits of wine ; except that it 

 immediately becomes opaque at the first touch of the flame, and 

 melts almost without becoming incandescent, changing to an 

 opaque mass of a brownish colour. 



c. The same is to be observed on applying a piece to the 

 flame of a wax or tallow candle. 



d. Exposed to the blow-pipe it melts instantaneously. 



e. When mixed with borax and carbon, and exposed to the 

 flame of the blow-pipe, it first of all effervesces veiy strongly like 

 the sulphates, and is afterwards dissolved, exhibiting a clear mass 

 slightly tinged with a yellowish brown. But if too much satu- 

 rated, it becomes opaque and white. 



f. In order to ascertain whether the changes which the fossil 

 suffered during calcination as to colour, transparency, and cohe- 

 rence, were produced merely by the loss of the v/ater of crystal- 

 lization, or whether they are to be attributed to the dispersion of 

 other of its component parts by heat, 10 grms. of polyhalite broken 

 into fragments were put into a small glass retort, to which was 



