132 MEMOIR ON THE SCIENTIFIC CHARACTER 



He gives the native characters of the ore, its reactions 

 before the blow-pipe and the action of reagents upon it^ 

 particularly of a delicate test of the presence of sulphur^ 

 which consisted in placing a minute portion of an insoluble 

 sulphate of baryta formed by treating its solution with 

 chloride of baryum on a very small bit of charcoal, heating 

 it strongly, then dipping it in a drop of water on polished 

 silver, giving to the latter a deep black stain. 



Mr. Smithson conducted his researches on a minute scale. 

 The above trials were made with particles little more than 

 visible; the results, however, sufficiently established the 

 nature of the constituent parts. The proportions were nec- 

 essarily left for inquiries on another scale. 



The two preceding subjects are honorably noticed in a 

 historical sketch of improvements in physical science dur- 

 ing the year 1819, contained in the 16th vol. of the Annals, 

 (1820,) p. 100. 



10. In the same vol. (xvi.) of the Annals, are contained 

 two letters to Dr. Thomson, one dated Paris, March 17th, 

 the other March 24th, 1820. 



The former contains a " View of the probable causes which 

 produce fibrous metallic copper, found both in the ores of copper ^ 

 and in the slag of copper furnaces." Mr. Smithson conceives 

 these fibres to be produced by squeezing metallic copper in 

 a state of fusion into or through pores of the glass, while 

 the latter is cooling and contracting. 



11. The latter communication contains An account of a 

 native combination of sulphuret of barium and fluoride of cal- 

 cium. This substance was found in Derbyshire, in close 

 proximity with sulphuret of lead. 



Ho describes with great minuteness the reaction of this 

 substance with tests, and infers that it consists of — 



Sulp. of Barium, . . - 51.5 



Fluoride of Calcium, - - - 48.5 



12. In the Annals, vol. xvii., p. 271, is a letter from Mr. 

 Smithson, dated February 17, 1821, in which he describes 

 capillary metallic tin forced through the pores of cast iron. 



13. In the Annals for August, 1822, vol. xx., p. 127, is an 

 article (Art. v.) On the detection of very minute quantities of ar- 

 senic and mercury. 



In this publication he refers to his paper in the Annals 

 for August, 1819, relative to the compound sulphuret of 

 lead and arsenic. 



