WRITINGS OP JAMES SMITHSON. 67 



fiulphate of soda, and correspond to 1.86 grains of it in an 

 arid state, or uncombined with ice.* 



10 grains of the saline part of this native salt would have 

 produced 1.12 grains of ignited muriate of silver (/c). By 

 accurate experiments 241 grains of ignited muriate of silver 

 have been found to correspond to 100 grains of ignited mu- 

 riate of soda.f 



Consequently the soluble portion of the present Vesuvian 

 ealt consists of 



Sulphate of potash - - 7.14 



Sulphate of soda - - 1.86 



Muriate of soda - - 0.46 



Muriate of ammonia ^ 



Muriate of copper I - - . o.54 

 Muriate of iron J 



10.00 

 t. The insoluble sandy residue (jg) having been thoroughly 

 •edulcorated, dilute nitric acid was put to it. A green solu- 

 tion formed without any effervescence. Acetate of barytes 

 scarcely rendered this solution turbid ; but nitrate of silver 

 produced a copious curd-like precipitate, and iron abund- 

 antly threw down copper from it. The green grains enclosed 

 in this native sulphate of potash, appear, therefore, to be a 

 flubmuriate of copper, of the same species as that of the 

 green sands of Peru and Chili. 



Muriatic acid dissolved the yellow ochraceous powder, 

 and prussiate of soda-and-iron produced Prussian blue. I 

 am inclined to believe this yellow powder to be a submu- 

 riate of iron, but its small quantity, and the admixture of 

 the submuriate of copper, were impediments to entirely 

 satisfactory results. Such a submuriate of iron, though, if 

 I mistake not, overlooked by chemists, exists, for the pre- 

 •cipitate which oxygen occasions in solution of green muriate 

 of iron, contains marine acid. 



* Prof. Klaproth'8 Essays, Vol. 1, p. 282. 

 f Dr. Henry, Phil. Trans. 1810. 



