3G1' Mr. J. M. Wilson on the Readings of the Graduated Arc 



able could it be obtained of sufficient richness in copper to 

 warrant its exportation to Europe, as, by the action of hydro- 

 chloric acid, large quantities of chlorine are evolved, which might 

 be made available for the production of chloride of lime, and the 

 residual solution of chloride of copper would yield the metal in 

 a very pure state upon the introduction of metallic iron. Un- 

 fortunately, although the ore is plentiful, but small quantities 

 are obtained having the composition given above, the average 

 yield of copper scarcely exceeding 5 per cent. 



The following Table may serve to illustrate the composition 

 of some of the principal silicates of copper : — 



Composition. 



1. 



2. 



3. 



4. 



5. 



G. 



7. 



Oxide of copper 



Silica 



50-00 

 38-70 

 11-30 



44-94 

 34-83 

 20-23 



29-50 



52-20 



16-70 



1-20 



1200 50-10 

 75-90 28-20 

 10-10 19-10 



39-50 



28-21 



24-52 



2-80 



4-97 



24-71 



18-90 



15-52 



•23 



40-28 



Water 



Oxide of iron 



Alumina 



Lime and magnesia.. 

 Oxide of manganese. 



'2-00 



il-46 





100-00 



100-00 



99-60 



100-00 



98-86 



100-00 ! 99-64 



(1) Dioptase. 



(2) Chrysocolla 



(3) Bluish-green amorphous silicate. Chile (Domeyko). 



(4) Green silicate (Domeyko). 



(5) Black silicate (Domevko). 



(6) Blue silicate. Chile (Field). 



(7) Douhle silicate of copper and manganese. Chile (Field). 



It may be mentioned that these silicates are, under certain 

 circumstances, very advantageous to the smelter, especially when 

 he has to operate upon highly ferruginous ores, by combining 

 with the oxide of iron, and thus saving the sides of the furnace, 

 which would otherwise be much injured. None of them contain 

 either antimony or arsenic ; and the copper therefore, after the 

 necessary fusions, is exceedingly pure. 



St. Mary's Hospital Medical School, 

 Loudon, October 11, 1861. 



XLV. Note on the Readings of the Graduated Arc in Spectrum- 

 Analysis, and Distortion of the Spectrum. By J. M. Wilson, 

 B.A., Fellow of St. John's College, Cambridge, and Natural 

 Philosophy Master in Rugby School*. 



IN the ordinary apparatus for spectrum-analysis, the rays 

 passing along the axis of a fixed telescope and incident on 



* Communicated by the Author. 



