1820.] M. Stromeyer on Folyhalite. 431 



affixed a little receiver connected with a small mercurial appa- 

 ratus. 



On the application of heat, the polyhaUte soon became white, 

 and lost its former colour and transparency ; at the same time 

 little clouds appeared in the retort, which, being condensed like 

 dew, distilled down, and passed into the bottle fixed to the 

 retort ; yet, excepting that from the air contained in the vessels 

 being partly expelled by the fire, some elastic fluid escaped, 

 no other substance was given off, although the heat was aug- 

 mented to such a degree that the bottom of the retort began to 

 be fused, and the fossil in many places was melted so as to form 

 one mass with the glass. The liquid thus obtained from it 

 afforded only a few drops, and when examined proved to be a 

 pure distilled water. 



Hence it appears that the changes which the fossil undergoes 

 are to be attributed merely to the loss of the water of crystal- 

 lization. 



(B.) Experiments on PolyhaUte with Water. 



Water quickly affects polyhalite. On its being merely poured 

 over it without heat, being at all employed, small fragments of 

 the fossil are nearly taken up by this menstruum, as before ob- 

 served ; and on the application of a slight heat, the water 

 -dissolves more than two-thirds of it when in powder, leaving 

 a tasteless powder of a whitish-red colour. When boiled in 

 water, the fossil is almost completely dissolved, although not 

 ■without a great deal of trouble, and employing a considerable 

 quantity of the menstruum, nothing then remains, excepting 

 a small poition of a brownish dust, which will not at all dissolve 

 in water. 



b. The solution of polyhalite obtained from cold water is lim- 

 pid, and perfectly colourless. It is generally of a brackish 

 flavour. It does not change the colour of turnsole, or violets, 

 to red, neither does it restore a blue colour to paper stained with 

 tincture of turnsole, or darken paper dyed yellow by the roots of tur- 

 meric. When concentrated by heat, the solution becomes turbid, 

 and deposits pointed, tasteless crystals. Afterwards exposed to 

 a spontaneous evaporation, it produces prismatic crystals, trans- 

 parent, and possessing a brackish flavour similar to that of the 

 solution itself: these exhibit partly four-sided prisms furnished 

 ■with tetrahedral summits, partly hexagonal prisms, terminated 

 at either extremity with a hexagonal pyramid ; the former variety 

 of these crystals cracks when exposed to the air. 



The following are the observations I have made respecting the 

 effects of alkalies, acids, and other agents upon this solution. 



1. It instantly becomes turbid when mixed with a pure and 

 perfectly caustic potash, and deposits a white precipitate, which 

 is not dissolved by an addition of more potash, but is readily 

 absorbed without any effervescence by nitric acid, 



