9,1 



that is to decompose it. Very little practice will show 

 the proper strength of the ingredients to corrode a certain 

 depth in the glass, where the strokes were drawn. The 

 rising fames will etch another prepared glass, if placed so as 

 to receive them, and perhaps more regularly. The acid for 

 chemical purposes is commonly procured in a leaden ap- 

 paratus. 



I have figured two specimens of the most common ap- 

 pearance of fluor. The upper one deviates a little in form, 

 the middle cube being interrupted by the side ones, con- 

 tracting its upper part, so that the lower is much the 

 broadest. There are some crystals of what is commonly 

 called eighteen-sided quartz sticking about them, as usual 

 with fluor from Cumberland. 



The lower figure seems altogether of a fine deep purple., 

 but is only thinly coated, the inside being of an olive green a 

 The faces are remarkable for having signs of the laminae of 

 superposition, indicating four-sided pyramids, the apex of 

 which appears at the edges of the cubes where in contact. 

 Fig. i. shows a corner of one of the cubes replaced by six 

 minute triangular facets. 



The upper figure has some signs of superposition, though 

 scarcely more than scratches, giving the specimen a greasy 

 appearance. The hexangular cavity is where a crystal of 

 quartz had stuck, and shows that the side inserted was not 

 regular : hence it appears that the crystals of quartz are not 

 regularly eighteen- sided, their shape being interrupted by 

 the fluor. 



