WRITINGS OF JAMES SMITUSON. 73 



■wise affected : 5.4 grs. of tbis 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 100^ of carbonate of calcium. 



This fine powder, w^hich 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 con- 

 sequently inferable that its proximate principles are sulphate 

 of barium and fluoride of calcium. 



The following experiments were made to obtain some 

 idea of the proportions in which these two compound com- 

 ponents 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 en- 

 tirely dissolved. The mixture was then exhaled dry, and 

 ignited. The weight was now 7.85 grs. The increase had, 

 therefore, been as -j^. 



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 cor- 

 responded, two grs. of pure fluoride of calcium in subtile 

 powder were treated with sulphuric acid till the augmenta- 

 tion of weight ceased. The two grains had then become 

 ,3.65 grs.; accordingly the augmentation of weight was == 



■i.65 = tVV 



This Derbyshire mineral, therefore, consists of 



Sulphate of barium - - 51.6 



.' Fluoride of calcium - , -.„ ,^,, 48.6 



100.0 



