134 Mr. T. H. Henry on Francolite. 



inconclusive as to the presence of oxygen. However, from an 

 examination of the known basic chlorides of lead and copper, 

 it appears most probable that the true composition of the 

 mineral is represented by the following formula : — 



(PbCl + PbO) + (CuCl + CuO) + aq. 



No salt having this composition has, so far as I am aware, 

 been hitherto described. 



XVII. On Francolite^ a supposed New Mineral. 

 ByT. H. Heney, Esq., F.R.S.^ 



MR. BROOKE some years since received from Mr. 

 Nuttall some specimens of a mineral found at Wheal 

 Franco near Tavistock, Devon, which appeared to him and 

 to Mr. Brooke to differ in external characters from all the 

 substances with which they were acquainted, and it was con- 

 sequently provisionally named Francolite. 



It consists of small masses of irregularly formed and aggre- 

 gated crystals, apparently hexagonal prisms of considerable 

 lustre, and covering the matrix with a sort of mammillated sur- 

 face. It has lately been found in another mine in larger and 

 purer specimens, and I have at Mr. Brooke's request analysed 

 a part of one of these. 



A small crystal, perfectly free from the matrix, was found 

 by means of the blowpiple to contain lime and phosphoric acid, 

 and a portion reduced to powder and warmed with sulphuric 

 acid corroded glass strongly. Iron and manganese were also 

 detected ; but a very minute trace of chlorine was found. 



I determined with this mineral to employ the method lately 

 recommended by Prof. H. Rose for the quantitative separation 

 of phosphoric acid from all bases but alumina, by means of 

 nitric acid and metallic mercury. The crystals were reduced 

 to powder, and freed from the matrix (quartz with copper 

 pyrites) by treatment in a stoppered bottle with very dilute 

 nitric acid in the cold (one part of strong acid to nineteen of 

 water), in which the mineral was perfectly soluble. The solu- 

 tion was evaporated to dryness with metallic mercury in a 

 platinum dish heated by steam (the fluoride of calcium is 

 hereby decomposed and the fluorine dissipated), and the re- 

 mainder of the process conducted scrupulously according to 

 the directions given by Rosef. 



# Communicated by the Author. 



t Poggendorff's Jnnalen, March 1849; or Chemical Gazette, vol. vii. 

 p. 202-206. 



