'WRITINGS OF JAMES SMITHSON. 89 



A DISCOVERY OF CHLORIDE OF POTASSIUM IN 

 THE EARTH. 



From Thomson's Annals of Philosophy, Vol. XXII ; New Series, Vol. 

 VI, 1823, page 258. 



SIB : A RED ferruginous mass, containing veins of a white 

 crystalline matter, part of a block which was said to have 

 been thrown out of Vesuvius during a late eruption, was 

 brought to me, with a request that I would tell what it was. 



This red ferruginous rock was a spongy lava, in the sub- 

 stance of which was here and there lodged a crystal of 

 augite or pyroxene of Haiiy, or of hornblende. 



The white matter filled most of the larger cavities, and 

 was more or less disseminated through nearly the whole of 

 the mass. 



It had a saline appearance ; a tabular fracture could be 

 seen in it with a lens, and in some few places regular cubi- 

 cal crystals were discernible. 



I supposed it to be chloride of sodium, or muriate of am- 

 monia. 



Heated in a matrass, it decrepitated slightly, and melted, 

 but little or nothing sublimed. 



This white matter dissolved entirely in water. Laid on 

 silver with sulphate of copper, it produced an intense black 

 stain. 



Chloride of barium added to the solution caused only a 

 very slight turbidness, due probably to some sulphate of 

 lime which is present. 



Tartaric acid occasioned an abundant formation of crys- 

 tals of tartar. Chloride of platinum immediately threw 

 down a precipitate, and distinct octahedral crystals of the 

 Bame nature afterwards appeared. 



On decomposition by nitric acid, only prismatic crystals 

 of nitrate of potash could be perceived. On a second crys- 



