74 WRITINGS OF JAMES SMITHSON. 



Some error is created by the admixed carbonate of lime ; 

 and which had not been removed. 



This mineral presents us with a remarkable case of com- 

 bination ; that of a neutral salt with a body which is not a 

 salt, but belongs to an order which is analogous to metallic 

 oxides. I have met with another instance of the same 

 kind. I have examined transparent crystals which were 

 composed of anhydrous sulphate of calcium and chloride 

 of sodium. 



These combinations of their compounds may, however, 

 perhaps, appear to some persons to cast doubts on the 

 opinion that chlorine and fluorine are not acids. 



These compounds will still be deserving of particular 

 attention from consisting of four matters. 



ON SOME CAPILLARY METALLIC TIN. 



From Thomson's Annals of Philosophy, Vol. XVII — New Series, 

 Vol. I— 1821, p. 271. 



Paris, February 17, 1821. 



Sir : M. Ampere, a few days ago, accidentally in conver- 

 sation, mentioned a fact to me which much excited my 

 attention, as it appeared to me completely to confirm the 

 explanation I had ventured to offer of the mode of forma- 

 tion of the capillary copper in the slag of the Hartz, printed 

 in the Annals of Philosophy for July, 1820. 



For some purpose of the arts, Mr. Clement formed a 

 cylinder of copper, and, to give it strength, introduced into 

 it a hollow cylinder, or tube, of cast-iron. To complete 

 the union of these two cylinders some melted tin was run 

 between them. With the exact particulars of this construc- 

 tion, I am not acquainted, but the material circumstance is, 

 that during the cooling of this heated mass, a portion of 

 the melted tin was forced by the alteration of volume of 



