90 WRITINGS OF JAMES SMITHSON. 



tallization, a few rhombic crystals were discovered ; but 

 nitrate of potash sometimes presents this form. 



It appears from these experiments, that this white saline 

 matter is pure, or nearly pure, chloride of potassium. 



I am inclined to attribute its introduction into the lava to 

 sublimation. 



As chloride of potassium is a new species in mineralogy, 

 I shall send the specimen to the British Museum. 



A METHOD OF FIXING PARTICLES ON THE 



SAPPARE. 



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

 VI, 1823, page 412. 



October 24, 1823. 



SIR : "When the species of minerals are ascertained by 

 their physical qualities, they mostly undergo no injury, or 

 but a very slight one ; as that attending the determination 

 of their hardness, the colour of their powder, their taste, 

 &c. This is certainly a material advantage, and would 

 highly recommend this method, was it constantly adequate 

 to its purpose. That it is not so, however, we have a proof 

 in the great errors into which have fallen those best skilled 

 in it. Mr. Werner, its principal and most distinguished 

 professor, was unable by its means to discover the identity 

 of the jargon and the hyacinth ; of the corundum and the 

 sapphire ; of his apatite and his spargelstein ; and while he 

 thus parted beings, as it were, from themselves, he forced 

 others together which had nothing in common. 



The chemical method justly boasts its certainty; but it 

 carries destruction with it, and often bestows the knowledge 

 of an object only at the expense of its existence. The sole 

 remedy which can be opposed to this defect is to reduce the 



