258 Discovery of Chloride of Potassium in the Earth. [Oct- 



tained, founded on any circumstance arising out of the Dublin 

 observations, that doubt must relate, not to the accuracy of 

 former catalogues, but to the present position of the stars ; since 

 it is with respect to their presew^ position that the two instru- 

 ments are really at variance. This circumstance is very fortu- 

 nate, as time may confirm the present, or suggest some more 

 satisfactory method of investigation, if what I have now 

 advanced be not thought sufficient for the purpose. 



AllTICLE IV. 



A Discovery of Chloride of Potassium in the Earth, 

 By James Smithson, Esq. FRS. 



(To the Editor of the Annals of Philosophy.) 

 SIR, 



A RED ferruginous mass, containing veins of a white crystal- 

 line 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 substance 

 of which was here and there lodged a crystal of augite or pyrox- 

 ene of Haliy, 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 cubical crystals 

 were discernible. 



I supposed it to be chloride of sodium, or muriate of ammonia. 



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 crystals of 

 tartar. Chloride of platinum immediately threw down a preci- 

 pitate, and distinct octahedral crystals of the same nature after- 

 wards appeared. 



On decomposition by nitric acid, only prismatic crystals of 

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

 tion, a few rhombic crystals were discovered ; but nitrate of 

 potash sometimes presents this form. 



i 



