1820.] and Fluoride of Calcium. 49 



colourless glass, which became opaque, and white on adding 

 more of it. 



A particle of this stone which had heen fused on the charcoal 

 being laid in a drop of water on a plate of silver, immediately 

 made a black spot of sulphuret of silver on it. 



This bit of melted stone, transferred to a drop of marine acid, 

 on a piece of glass, partially dissolved with effervescence. The 

 solution let exhale spontaneously, afforded crystals of chloride of 

 barium. 



Some of this stone in fine powder, being heated in a drop of 

 sulphuric acid on a bit of glass, the polish of the glass was 

 destroyed. 



Water in which this stone in fine powder had been boiled was 

 not affected by solution of nitrate of lead. 



A bit of this stone, being heated in dilute marine acid, emitted, 

 a few bubbles of carbonic acid, but was not otherwise affected : 

 5*4 grs. of this mineral in very fine powder were let remain in an 

 excess of marine acid till all action on them had ceased. The 

 undissolved portion washed and gently ignited weighed 5*15 grs. 

 The acid had acquired lime ; so that this mineral contains a 



mechanical admixture of of carbonate of calcium. 



This fine powder, which had been treated with the marine 

 acid, had sulphuric acid evaporated to dryness on it in a platinum 

 crucible. It was then digested in dilute marine acid. On 

 evaporating this solution, a large quantity of sulphate of calcium 

 in crystals was obtained. 



From these results, sulphuric acid, fluorine, barytes, and lime, 

 appear to be the elements of this mineral. It is consequently 

 inferable that its proximate principles are sulphate of barium and 

 flporide of calcium. 



The following experiments were made to obtain some idea of 

 the proportions in which these two compound components of 

 this mineral exist in it : 



5'6 grs. of this stone in powder were heated in a platinum 

 crucible in so large a quantity of sulphuric acid as to be entirely 

 dissolved. The mixture was then exhaled dry, and ignited. 

 The weight was now 7-85 grs. The increase had, therefore, 



been as — . 



100 



This augmentation of weight could arise only from the change 

 of the fluoride of calcium into sulphate of calcium. 



To know to what quantity of fluoride of calcium it corres- 

 ponded, two grs. of pure fluoride of calcium in subtile powder 

 were treated with sulphuric acid till the augmentation of weight 

 ceased. The two grains had then become 3'65 grs. ; accord- 



ingly the augmentation of weight was = 1"65 = — . 



i_ This Derbyshire mineral, therefore, consists of 

 Vol. XVI. N° I. D 



